tag:blogger.com,1999:blog-41679145491234712122024-03-13T15:43:28.961-04:00Living LIGOAmber Stuver's day-to-day life as a LIGO scientist<br>
<a href="http://www.LivingLIGO.org">www.livingLIGO.org</a><br>
Follow me on Twitter: <br>
<a href="http://www.twitter.com/livingligo">www.twitter.com/livingligo</a>stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comBlogger103125tag:blogger.com,1999:blog-4167914549123471212.post-34458264230937065832017-10-16T10:05:00.000-04:002017-10-16T11:12:31.689-04:00First Observation of a Neutron Star with Gravitational Waves and Light! <b>THE OBSERVATIONS </b><br />
<b></b><br />
At about 8:41 am EDT on 17 August 2017, both LIGO observatories recorded a
100-second long gravitational wave (GW) signal that appeared to be coming from
two <a href="https://en.wikipedia.org/wiki/Neutron_star">neutron stars</a> orbiting each other and merging together (this detection is called GW170817). 1.7 seconds
later, the <a href="https://en.wikipedia.org/wiki/Fermi_Gamma-ray_Space_Telescope">Fermi Gamma Ray Burst Monitor</a> detected a short <a href="https://en.wikipedia.org/wiki/Gamma-ray_burst">gamma-ray burst</a>
(GRB). LIGO's online data analysis, along with Virgo not detecting the
event due to its location in a part of the sky it isn't sensitive to, narrowed
down the possible location of the gravitational wave source to the constellation
<a href="https://en.wikipedia.org/wiki/Hydra_%28constellation%29">Hydra</a> (in the Southern Hemisphere) which overlapped with the area determined
from the GRB detection. Both the LIGO and GRB detectors put out circulars
alerting the astronomy community to the independent discoveries; an event like
this was unprecedented and became a priority target for observation. LIGO
also produced a luminosity distance (a method of estimating the distance to the
source) of about 130 million light-years.<br />
<br />
11 hours after the gravitational wave and GRB detections (the delay was
caused by the time it took for the Earth to rotate observatories in South
America into their nighttime sky), the 1-m <a href="http://obs.carnegiescience.edu/swope">Swope Telescope</a> in Chile observed a
new point of light (referred to as a transient) from galaxy <a href="https://en.wikipedia.org/wiki/NGC_4993">NGC 4993</a>, also
about 130 million light-years away! Approximately 70 other observatories, both on our
planet and orbiting it, observed this new source of light: 11.5 hours after
GW/GRB detection, infrared light was observed; 15 hours later, ultraviolet
light was observed; as the days went on, the optical light from the source became
redder (longer wavelength) and dimmer than the early days; 9 days later, x-rays
were observed; 16 days later, radio waves were observed.<br />
<div class="separator" style="clear: both; text-align: center;">
</div>
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://3.bp.blogspot.com/-uhChJtbw9oE/WeQpkM2jrJI/AAAAAAAADXQ/SFrpKCe8SYIVxrJP7WY9r1EE9l-yxkZmQCLcBGAs/s1600/data.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="586" data-original-width="1600" height="182" src="https://3.bp.blogspot.com/-uhChJtbw9oE/WeQpkM2jrJI/AAAAAAAADXQ/SFrpKCe8SYIVxrJP7WY9r1EE9l-yxkZmQCLcBGAs/s400/data.png" width="500" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b><span style="color: #e69138;">CLICK TO ENLARGE!</span></b><br />
Left: GRB data (top) collected by Fermi and gravitational wave data (bottom) collected by LIGO.<br />
Right: Source localization on the sky from the INTEGRAL GRB satillite (light blue band), Fermi (the dark blue disk), LIGO alone (green ovals), and LIGO and VIRGO data combined (dark green oval). Notice that all sources identified the LIGO-Virgo area. A new source of light (located at the intersection of the tic marks) was identified inside the overlapping area by the Swope telecope (top image inset). The image below the inset is of the same area but 20.5 days before this event showing that this source was not present. [Credit: LIGO, Virgo, Fermi, Swope, DLT40]</td></tr>
</tbody></table>
<br />
<br />
<b>TURNING OBSERVATIONS INTO MEANING</b><br />
<br />
The cause(s) of <a href="https://en.wikipedia.org/wiki/Gamma-ray_burst#Short_gamma-ray_bursts">short GRBs</a> have been the subject of much theoretical
research; the predominant theory is that they are caused by the merger of two
neutron stars or a neutron star and a black hole. The problem is that
light isn't capable of bringing us information about these kinds of
systems. So, we've seen many short GRBs, we have ideas about how they are
made based on these observations, and have been waiting for evidence to either
support or refute the theory. Fortunately, gravitational waves bring us
the information about the system that light can't, like the masses of the
objects and how they moved around each other. <span style="color: #e69138;"><b>This is the first
conclusive evidence that at least some of the short GRBs are created by neutron
star mergers.</b></span><br />
<div class="separator" style="clear: both; text-align: center;">
<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/e8Yt7O7BLuc/0.jpg" frameborder="0" height="416" src="https://www.youtube.com/embed/e8Yt7O7BLuc?feature=player_embedded" width="500"></iframe></div>
<div style="text-align: center;">
<span style="color: #999999;"><span style="font-size: small;">This visualization shows the coalescence of two orbiting neutron stars.
The left panel contains a visualization of the matter of the neutron
stars. The different colored layers are different densities, which have
been made transparent to show more structure. The right panel shows how
space-time is distorted near the collisions. The spiral wave distortions
at the end of the merger propagate to Earth and are measured as
gravitational waves. [Credit: (taken from <a href="http://ligo.org/">ligo.org</a>) Christopher W. Evans/Georgia Tech] </span></span>
</div>
<br />
<br />
Light observations allowed us to observe the rapid fading of the brightness
and gradual lengthening of the wavelength (reddening) of the light which is a
signature of a <a href="https://en.wikipedia.org/wiki/Kilonova">kilonova</a> explosion. Kilonovae are also thought to be the
source of most of the heavy elements in the universe. (<a href="http://stuver.blogspot.com/2013/12/silver-and-gold-clues-to-history-of-our.html">I have previouslyattributed these to supernova here</a>; further research has shown that
while a supernova can make some heavy elements, it can't make enough of the
heavier ones like gold to account for the amounts we have.) Breaking the
light down into its different wavelengths (colors) tells us about the
composition of the source or of elements being created. Measurements like
this showed that <a href="https://en.wikipedia.org/wiki/Nucleosynthesis">heavy elements were indeed created</a> as predicted in this
kilonova and supports that <span style="color: #e69138;"><b>neutron star mergers may very well be the source
of most of the heavy elements in the universe.</b></span><br />
<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><img border="0" data-original-height="1121" data-original-width="1600" height="350" src="https://3.bp.blogspot.com/-E7ORbH1WxX4/WeQ8mi1Q_mI/AAAAAAAADYE/j2IKeBuqNBgP9e_B8AXrdgeivhxjkf-TQCEwYBhgL/s320/periodic_table.png" width="500" /></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Periodic table indicating the sources of the elements. <span style="color: #e69138;">Orange</span> indicates formation from the merger of neutron stars like the source of GW170817. [Credit: <a href="http://blog.sdss.org/2017/01/09/origin-of-the-elements-in-the-solar-system/">Jenifer Johnson</a>]</td></tr>
</tbody></table>
<br />
<br />
<span style="color: #e69138;"><b>The timing of the arrival of gravitational waves and the gamma-ray burst
(1.7 seconds later) are our strongest support yet that gravitational waves
travel at the speed of light.</b></span> Detecting gravitational waves first is
not unexpected since this system has been producing gravitational waves its
whole life and we only saw the last 100 seconds of it. It is the dynamics
of what happens during the merger that produces the light in the form of a GRB,
so we should expect a delay. Even when considering different possible
ways and times for light to be made in a system like this, our observations are
consistent with the prediction that gravitational waves travel at the speed of
light.<br />
<br />
<br />
<b>WHAT DID THIS NEUTRON STAR MERGER CREATE?</b><br />
<br />
A remaining question that the observations we've made hasn't been able to
answer is: What did this neutron star merger create: a very large neutron star
or a <a href="https://en.wikipedia.org/wiki/Black_hole">black hole</a>? We simply don't know and the reason why is that we don't
have a firm understanding of the <a href="https://en.wikipedia.org/wiki/Equation_of_state">equation of state</a> (EOS) for a neutron star
(EOS is a technical term for describing matter and how it behaves).
Depending on different possible EOSs, we can get either a small black hole or a
very massive neutron star at some time after the merger. We also looked
for gravitational wave evidence of which it is since a small black hole would
have produced gravitational waves at about 6000 Hz and a very massive neutron
star would produce them up to 4000 Hz. The LIGO detectors are not
very sensitive at high frequencies, making finding evidence for a resultant
black hole impossible. We did search for gravitational waves consistent
with the formation of a very massive neutron star until the end of the run on
25 August (8 days later) and didn't find anything. We found nothing to
support either possibility so we simply don't know!<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-3QefrdFxvXo/WeQrsJnCEpI/AAAAAAAADXo/MBZSxlfBqBw6rgntQm-eYBZ-KFduahfCgCLcBGAs/s1600/Mass_plot_black_no_gap.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1333" data-original-width="1600" height="414" src="https://1.bp.blogspot.com/-3QefrdFxvXo/WeQrsJnCEpI/AAAAAAAADXo/MBZSxlfBqBw6rgntQm-eYBZ-KFduahfCgCLcBGAs/s400/Mass_plot_black_no_gap.png" width="500" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The masses of
stellar remnants are measured in many different ways. This graphic shows
the masses for black holes detected through electromagnetic
observations (purple); the black holes measured by gravitational-wave
observations (blue); neutron stars measured with electromagnetic
observations (yellow); and the masses of the neutron stars that merged
in an event called GW170817, which were detected in gravitational waves
(orange). The remnant of GW170817 is unclassified, and labeled as a
question mark. [Credit: LIGO-Virgo/Frank Elavsky/Northwestern
University]</td></tr>
</tbody></table>
<br />
<br />
<br />
<b style="mso-bidi-font-weight: normal;">THIS IS JUST THE START!</b><br />
<br />
This is the true beginning of multi-messenger astronomy! As was
referred to in this post, gravitational waves, light, and neutrinos (looked for
during this event but none were found) bring us different information about the
universe. Gravitational waves tell us about how mass moves around and how
much of it there is; light tells us about temperature, and composition;
<a href="https://en.wikipedia.org/wiki/Neutrino_astronomy">neutrinos</a> can bring us information about the nuclear reactions happening deep
within a star. The effort to make and share all of these observations
require not just scientific knowledge, but cooperation on a large scale. <span style="color: #e69138;"><b>There
are many things that divide us in our societies; this is something we should be
proud to unite us!</b></span><br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://3.bp.blogspot.com/-ALQ9mlbbdtk/WeQsmkoq_hI/AAAAAAAADX4/JaowQS7-xZElmTzg31zaB3kMxhZoUreiQCEwYBhgL/s1600/GW170817gridSmlCrop.jpeg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1600" data-original-width="1433" height="560" src="https://3.bp.blogspot.com/-ALQ9mlbbdtk/WeQsmkoq_hI/AAAAAAAADX4/JaowQS7-xZElmTzg31zaB3kMxhZoUreiQCEwYBhgL/s320/GW170817gridSmlCrop.jpeg" width="500" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Artist’s illustration of two merging neutron stars. The rippling
space-time grid represents gravitational waves that travel out from the
collision, while the narrow beams show the bursts of gamma rays that are
shot out just seconds after the gravitational waves. Swirling clouds of
material ejected from the merging stars are also depicted. The clouds
glow with visible and other wavelengths of light. [Credit:
NSF/LIGO/Sonoma State University/A. Simonnet]</td></tr>
</tbody></table>
stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.com800 Lancaster Ave, Villanova, PA 19085, USA40.0379514 -75.342615940.0364319 -75.3451374 40.0394709 -75.3400944tag:blogger.com,1999:blog-4167914549123471212.post-58107803046959349772017-09-14T11:24:00.001-04:002017-09-14T11:26:41.388-04:00Second Anniversary of the First Detection and a New Job!<a href="https://4.bp.blogspot.com/-7JYWwoxKaSQ/Wbnen7nSfqI/AAAAAAAADTQ/o9MmjGk4bYo3sMqYqhw1cj4U7eG0pDe0gCLcBGAs/s1600/1024px-Villanova_University_Seal.svg.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="1024" data-original-width="1024" height="200" src="https://4.bp.blogspot.com/-7JYWwoxKaSQ/Wbnen7nSfqI/AAAAAAAADTQ/o9MmjGk4bYo3sMqYqhw1cj4U7eG0pDe0gCLcBGAs/s200/1024px-Villanova_University_Seal.svg.png" width="200" /></a>While posts here have been long awaited, I've been busy doing research, teaching, and changed my job! I've just started a new job as an assistant professor at <a href="http://www1.villanova.edu/main.html">Villanova University</a> and an academic job search is quite intensive (perhaps I will write about finding a faculty job soon). Also, I've been writing some other things. I've written a <a href="https://ed.ted.com/">TED-Ed</a> video/lesson on gravitational waves and it premiers today (you can view it <a href="https://ed.ted.com/lessons/what-are-gravitational-waves-amber-l-stuver">here</a>), I have a <a href="http://iopscience.iop.org/bookListInfo/physicsworld-discovery">PhysicsWorld Discovery</a> text on "Gravitational Waves" coming soon, and have written a few other things here and there. So, now that I've moved from Baton Rouge to the suburbs of Philadelphia, I have some time to talk with all of you again.<br />
<br />
<br />
<br />
<b>ANNIVERSARY OF GW150914: WHERE IS IT NOW?</b><br />
<br />
Today is the second anniversary of the first detection of gravitational waves. That got me thinking of about where the front of that wave is now...<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-RTo9Ydx5t6M/Vrrh-B-MoII/AAAAAAAAB0c/w9OG6XInxskoZmxTnLgbjwFaz4fWf_oGgCPcBGAYYCw/s1600/skylocation_galaxy_preview.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="800" data-original-width="1600" height="200" src="https://4.bp.blogspot.com/-RTo9Ydx5t6M/Vrrh-B-MoII/AAAAAAAAB0c/w9OG6XInxskoZmxTnLgbjwFaz4fWf_oGgCPcBGAYYCw/s400/skylocation_galaxy_preview.jpg" width="500" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>The colored area on this map shows the most probable source of the
detected gravitational wave where red is more likely than purple. The
location is shown against a map of the night sky centered on the Milky
Way galaxy with constellations outlined. </b><br />
[Credits: NASA Deep Star Maps (Visualization Credits, Ernie Wright (USRA): Lead
Animator, Tom Bridgman (GST): Animator) by NASA/Goddard Space Flight
Center Scientific Visualization Studio with constellation figures based
on those developed for the IAU by Alan MacRobert of Sky and Telescope
magazine (Roger Sinnott and Rick Fienberg), and the source location
based on Gravoscope screen grabs (LIGO & Nick Risinger, <a href="http://skysurvey.org/" target="_blank">skysurvey.org</a>), all in galactic coordinates. Composition by University of Florida / S. Barke.]</td></tr>
</tbody></table>
<br />
The source of <a href="http://stuver.blogspot.com/2016/02/LIGO-FirstDetection.html">GW150914</a> was from the general vicinity of the constellations <a href="https://en.wikipedia.org/wiki/Volans">Volans</a> and <a href="https://en.wikipedia.org/wiki/Carina_%28constellation%29">Carina</a>. That means that it is traveling towards the stars in the constellation <a href="https://en.wikipedia.org/wiki/Draco_%28constellation%29">Draco</a>. It hasn't encountered much. Since it has traveled a distance of 2 light years from Earth, it is still in our <a href="https://en.wikipedia.org/wiki/Milky_Way">Milky Way galaxy</a> (the radius of the Milky Way 60,000 is ly and its disk is 2000 ly). It has not encountered any other stars (the closest star in Draco is <a href="https://en.wikipedia.org/wiki/Struve_2398">Struve 2398</a>, a binary system of <a href="https://en.wikipedia.org/wiki/Red_dwarf">red dwarf</a> stars 11.6 ly away) and therefore no other planets. That means that no other life forms have detected GW150914 and won't reach Struve until early 2027 (give or take for the error in our understanding of its distance).<br />
<br />
<br />
<b>THE THIRD DETECTION: GW170104</b><br />
<br />
Since I wrote last, we announced the discovery of a third detection of gravitational waves from another binary black hole system dubbed <a href="http://ligo.org/science/Publication-GW170104/index.php">GW170104</a>. A black hole 32 times the mass of our Sun merged with another black hole 19 times the mass of our Sun resulting in a single 49 solar mass black hole after radiating away 3 solar masses in gravitational waves. Among other things, this detection helps to fill in the range of masses we've observed; gaps would imply that there is something preventing the formation of those kinds of systems and that would be unexpected. <br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-6xWxIP7LeEA/WbnfNG4CG3I/AAAAAAAADTY/tzQvQagF60s9PGHNLXHcgH9zu8DaoVoFACLcBGAs/s1600/BHmassChartGW17.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1108" data-original-width="1600" height="276" src="https://2.bp.blogspot.com/-6xWxIP7LeEA/WbnfNG4CG3I/AAAAAAAADTY/tzQvQagF60s9PGHNLXHcgH9zu8DaoVoFACLcBGAs/s400/BHmassChartGW17.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Graphic representation of the known stellar mass black holes observed through X-ray observations (purple) and gravitational waves (blue).</b> [credit: LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)]</td></tr>
</tbody></table>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
TESTING GENERAL RELATIVITY <br />
<br />
This system originated from about 3 billion light-years away: farther
out in the universe than any of our previous detections. Using a
gravitational wave that has traveled such a distance allows us to test a
part of general relativity that we haven't been able to before: do
gravitational waves <a href="https://en.wikipedia.org/wiki/Dispersion_%28optics%29">disperse</a>? For example, when white light enters a
prism, the different colors (frequencies) of light travel at slightly
different speeds causing them to separate or disperse. General
relativity predicts that different frequencies of gravitational waves
should not disperse. There are alternate theories of gravity that make
predictions of how dispersion will affect a gravitational wave. We
compared our observation to standard general relativity and the
alternate theories' predictions and found our observations to be
consistent with general relativity. That is, we did not observe any
significant dispersion of our gravitational wave! We've also done all
of the tests of general relativity that were done for the previous
detections and this gravitational wave continues to affirm that general
relativity is correct.<br />
<br />
MEASURING SPIN TO INVESTIGATE BLACK HOLE FORMATION <br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-kUUe6g06fPI/WbnnivlE0LI/AAAAAAAADTo/1PsrQHoDlwE6yIQG1HtiWhkQfOADC1zggCLcBGAs/s1600/BlackHoleArt.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1280" data-original-width="1600" height="320" src="https://2.bp.blogspot.com/-kUUe6g06fPI/WbnnivlE0LI/AAAAAAAADTo/1PsrQHoDlwE6yIQG1HtiWhkQfOADC1zggCLcBGAs/s400/BlackHoleArt.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>Artist's conception shows two merging black holes similar to those
detected by LIGO. The black holes are spinning in a non-aligned fashion,
which means they have different orientations relative to the overall
orbital motion of the pair. LIGO found hints that at least one black
hole in the system called GW170104 was non-aligned with its orbital
motion before it merged with its partner.</b> Credit:
LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)</td></tr>
</tbody></table>
<br />
We also were able to investigate the spin of the black holes. For as mind-blowing as a black hole is, it is completely described by three numbers: 1) its mass, 2) its spin, 3) its charge (this is postulated by the <a href="https://en.wikipedia.org/wiki/No-hair_theorem">no-hair theorem</a>). Since we believe the electric
charge of astrophysical black holes to be negligible, physicists get
very excited about the mass and the spin. The mass is not too hard to
measure (we can get that pretty accurately from the waveform shape and
frequency evolution), but the spin is all in the details of the signal
which makes it more difficult to estimate. But we always still mention
it because any information we get about it will tell us more about the
other half of the back hole's story.<br />
<br />
For this detection, we were able to extract information about how the combined spin of the
black hole system compares to the direction of its orbital angular
momentum. Basically, does the direction the effective spin of the black
holes (on their internal axes) go in the same direction as their orbit?
For example, the Earth spins on its axis in the same direction as
it orbits the Sun, so this is a positive alignment, but the Earth's axis
is tilted so it isn't a perfect alignment. <br />
<br />
If most of our black hole systems have small misalignments that would
support their formation through something we call "<a href="https://en.wikipedia.org/wiki/Common_envelope">common envelope evolution</a>" (I wrote about this <a href="http://stuver.blogspot.com/2016/04/the-source-of-gw150914-stellar-mass.html">here</a>), which is a complicated way of saying that the stars that
formed the black holes were always paired together and once they both
died you end up with a binary black hole system. The interactions
between those original stars will cause their spins to align giving the
resulting binary black hole system only small misalignments.<br />
<br />
Another
formation mechanism for binary black holes is that they just happened
to pass one another while drifting through space and became
gravitationally bound together (this is called dynamical assembly). We
expect things like this to happen in dense stellar clusters or near the
centers of galaxies. Since these would have had no interaction with
each other before they became a system, we expect random spin alignments
from the black holes.<br />
<br />
Ultimately we found that our system likely
had a low total spin and was likely not aligned with the orbital
angular momentum of the system. It is also possible that our black
holes had no spin to begin with. So this isn't definitive, but we are starting to assemble the story of how black hole systems like this form.<br />
<br />
<br />
<b>THE BIG PICTURE</b><br />
<br />
With this discovery, we are adding to our understanding of the universe
and testing general relativity in ways we've never been able to before.
The importance is that LIGO is truly operating as an observatory
(that's what the 'O' in LIGO stands for after all) and building a
database of observations. In astronomy, you can never make a single
observation and understand a system's history. You need to take a large
sample of observations from similar systems and find out what the
patterns are. That's how we understand how stars evolve since a human
life, or even all of human existence, isn't long enough to have followed
a single star's life cycle. But because we have observed many stars in
different stages of their lives we've discovered patterns. That's how
we know that the black holes we just observed are the collapsed corpses
of the extremely massive stars. Now we can collect observations of many
of these black hole systems to learn more about black holes in general
and how these pairs of black holes form.stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.com800 Lancaster Ave, Villanova, PA 19085, USA40.037056 -75.34357999999997414.5150215 -116.65217399999997 65.5590905 -34.034985999999975tag:blogger.com,1999:blog-4167914549123471212.post-7054514539182935342016-06-15T13:23:00.001-04:002016-06-15T15:40:36.507-04:00Merry Christmas, LIGO: Another Gravitational Wave!<span style="font-size: large;"><b>WE DETECTED ANOTHER GRAVITATIONAL WAVE!</b></span><br />
<br />
On the evening of <span style="color: #38761d;">Christmas day 2015, at 9:38 pm CST (3:38 am UTC)</span> at the LIGO Livingston Observatory in Louisiana, another gravitational wave signal was recorded. <span style="color: #38761d;">1.1 ms later</span>, the LIGO Hanford Observatory in Washington state also picked up the same signal. <span style="color: #38761d;">70 seconds later</span>, the supercomputer that runs analyses on the near real-time data noticed that there was something special in the data and sent out emails and text messages that some of us affectionately call the "Bat Signal". This goes out to scientists primarily to summon those who evaluate candidate gravitational wave events to determine if this event should be shared with traditional astronomers (i.e. ones with telescopes). I am on the list because I am interested in keeping up on the latest results. I remember exactly where I was: I was in my room at my mother's house outside of <a href="https://en.wikipedia.org/wiki/Pittsburgh">Pittsburgh</a> changing clothes after getting back from visiting the in-laws (who live within a few miles of my family's home) for Christmas. I looked at the event record and saw that this was an extraordinary candidate gravitational wave in that its statistical significance was high but the signal wasn't as obvious in graphs as the first detection in September was.<br />
<br />
It was decided to send out the location of the possible detection to traditional astronomers and the emails started flying discussing the evidence that this was a true detection. It was determined that the preliminary information on the signal warranted starting the detection checklist - the large-scale investigations that try to disprove that the signal is real. Only after a candidate passes every test and has a high statistical significance is it accepted as a detection. The same checklist that was applied to <a href="http://stuver.blogspot.com/2016/02/LIGO-FirstDetection.html">the first detection, labeled GW150914</a>, was applied to this candidate as well. Once this Christmas detection was verified, it was labeled <span style="color: #38761d;">GW151226</span> (the number reflects the UTC date that the gravitational wave was discovered) although we had nicknamed it the "<a href="https://en.wikipedia.org/wiki/Boxing_Day">Boxing Day</a> Event" before the verification.<br />
<br />
(Below I will often refer to GW150914 as the "first detection" and GW151226 as the "new detection".)<br />
<br />
Read the paper on the detection <a href="http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.241103#fulltext">here</a>. <br />
<br />
<br />
<span style="font-size: large;"><b>THE SIGNAL & THE SOURCE</b></span><br />
<br />
The signal is similar to the first detected gravitational wave (GW150914). We call this kind of signal a "<a href="https://en.wikipedia.org/wiki/Chirp">chirp</a>" because initially it has a low frequency which increases over time as does its amplitude. You've heard signals like this before if you've ever hear a slide whistle increasing in tone. The increase in tone reflects the increase in frequency and the loudness of the whistle represents the amplitude. The signal we detected <span style="color: #38761d;">starts at about 35 Hz</span> (close to the frequency of the sound made by the second black key from the left on the piano) and <span style="color: #38761d;">reaches its highest frequency at about 450 Hz</span> (very close to the A above middle C if you convert this signal into sound).<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-ETfn2xSo7vM/V2DLl4iagdI/AAAAAAAACI0/MOWPUa55oZcNdu0bTL_zckrIPHZKGPbbQCLcB/s1600/GW151226-1.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="170" src="https://4.bp.blogspot.com/-ETfn2xSo7vM/V2DLl4iagdI/AAAAAAAACI0/MOWPUa55oZcNdu0bTL_zckrIPHZKGPbbQCLcB/s400/GW151226-1.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Graph of the 1-second signal of GW151226. The red line is the prediction of what a gravitational wave from a 14.2 and 7.5 solar mass black hole merger would look like and the grey area around it is the signal that LIGO recovered from its data. The zoomed in portions allow you to get a better look at hour the prediction (in red) and the actual signal (in grey) compare. At the end of this signal, the frequency and amplitude both go up. The two black holes merge at the point where the amplitude of the signal is the highest (seen in the zoomed data to the far right).</td></tr>
</tbody></table>
<br />
The plot above shows what we detected in our data compared to the predictions of a pair of black holes orbiting each other and merging into one. So this is <a href="http://stuver.blogspot.com/2016/02/LIGO-FirstDetection.html">similar to the last detection</a> in that this is also a pair of <a href="https://en.wikipedia.org/wiki/Stellar_black_hole">stellar-mass black holes</a> (formed from the death of extremely massive stars) but different because the masses of these new black holes are less than the first detection. Here, <span style="color: #38761d;">our newly detected black holes are 14.2 and 7.5 solar masses</span> where our last detection was 36.2 and 29.1 solar masses. That makes this signal weaker than the last (<span style="color: #38761d;">the peak amplitude of this new signal is about 1/3 that of the first detection</span>) but we are able to observe more orbits of the system here. <span style="color: #38761d;">We see about 27 orbits of these new black holes (corresponding to the 55 cycles of the gravitational wave we see in the figure)</span> where we only saw about 5 orbits (or 10 cycles) in the first detection. It is interesting to note that lower mass black hole pairs will merge at higher frequencies than higher mass black holes. This means that the signal will stay in LIGO's most sensitive frequencies longer and that is reflected in what we see here. <span style="color: #38761d;">This new detection's signal is about 1 second long</span> while the first detection is less than a half second long.<br />
<br />
So, what did this new detection look and sound like? As far as what it looked like, there was no light that we are aware of that was produced from this system. But we can visualize the black holes as they orbit around each other and track the corresponding progression through the signal to the merger. [Credit: SXS Collaboration/<a data-saferedirecturl="https://www.google.com/url?hl=en&q=http://www.black-holes.org&source=gmail&ust=1466091823643000&usg=AFQjCNF43LoND1VeGLi8kW_C0D6pkwcbLQ" href="http://www.black-holes.org/" target="_blank">www.black-holes.<wbr></wbr>org</a>]:<br />
<span style="font-family: "cambria"; font-size: 12.0pt;"></span><br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<iframe allowfullscreen='allowfullscreen' webkitallowfullscreen='webkitallowfullscreen' mozallowfullscreen='mozallowfullscreen' width='450' height='374' src='https://www.blogger.com/video.g?token=AD6v5dx5F1S-L3vn1x-jQ612utwzJ7P6D28MirRgN-mww6UdYZmua4izXWYkHM-XSdQGFbXtdQ4dxN0k1y0t_YyQOw' class='b-hbp-video b-uploaded' frameborder='0'></iframe></div>
<br />
<br />
We can also "listen" to gravitational waves by taking the signal, and converting it into sound through your speakers. Below is a comparison of what the new detection "sounded" like compared to the first detection. The actual "sounds" are quite low in tone so that they sound more like thumps. We also have shifted the sounds up to a higher tone so that you can hear more of the detail in the signals. That will play after the original lower tones. The background graph shows how the frequency changes on the vertical axis (you will see that it increases for both signals) as time progresses on the horizontal axis:<br />
<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<iframe allowfullscreen='allowfullscreen' webkitallowfullscreen='webkitallowfullscreen' mozallowfullscreen='mozallowfullscreen' width='320' height='266' src='https://www.blogger.com/video.g?token=AD6v5dzIlP4eneYFMJDwjIU4_g6cNGGY0C2pewG1ZPzZtWjl4P5NPQTGTrOAVXqpEuhdxcmhZkvvCs1vgcOOaLMe_g' class='b-hbp-video b-uploaded' frameborder='0'></iframe></div>
<br />
<br />
The next question is where in the sky are these black holes? We primarily determine this using the delay in detection time between the two detectors. When the delay is large, there is a smaller area in the shape of a ring on the sky where the gravitational wave could have come from. The detection delay for the new detection is much shorter than the first detection, so our uncertainty is going to be larger. Below is an illustration of the areas on the sky where the new detection (the area to the left) and the first detection (the area to the right) are likely to have come from. Note that for the new detection on the left, there is another similar area on the opposite side of the sky that cannot be seen in this image.<br />
<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-JouUNqJe7jg/V2DjxBEU1mI/AAAAAAAACJM/Pyug2uEF-DYPHhlrh7Mf4_CuzMoY02UmQCLcB/s1600/Localization%2BComparison%2B2a.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="320" src="https://4.bp.blogspot.com/-JouUNqJe7jg/V2DjxBEU1mI/AAAAAAAACJM/Pyug2uEF-DYPHhlrh7Mf4_CuzMoY02UmQCLcB/s320/Localization%2BComparison%2B2a.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The location of both the new GW151226 detection (on the left) and the first detection, GW150914 (on the right). These are pictured on a star map (you can see the center part of the Milky Way galaxy on the left and extending right). There is another similar area for the new detection on the opposite side of the sky (not pictured here). The outer purple area is where we are 90% confident where the sources are located. The inner circles each have decreasing certainty.</td></tr>
</tbody></table>
<br />
<br />
We will be better able to determine the location of a gravitational wave source on the sky when we have more than two detectors in operation. Fortunately, <a href="http://www.virgo-gw.eu/">Advanced Virgo</a> has completed their upgrades and is currently testing their new detector. LIGO's next observing run is expected in the 4th quarter of this year and Advanced Virgo will likely join the search before the completion of that run. When we detect more gravitational waves (which we expect since we will be even more sensitive than we were for the two detections we have already made and the run will be longer in duration) together with Virgo, we will know even more about what it is that we are seeing.<br />
<br />
This is an exciting time to be a scientist!<br />
<br />
Read the <a href="http://ligo.org/science/Publication-GW151226/index.php">official LIGO "Science Summary" on this new detection, GW151226</a>. stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comtag:blogger.com,1999:blog-4167914549123471212.post-9508107113694809132016-04-08T00:01:00.000-04:002018-04-24T13:06:12.830-04:00The Source of GW150914: Stellar Mass Black Holes<a href="http://stuver.blogspot.com/2016/02/LIGO-FirstDetection.html">On September 14th, 2015, LIGO made the first direct detection of gravitational waves.</a> This event is labeled <a href="http://stuver.blogspot.com/2016/02/LIGO-FirstDetection.html">GW150914</a> (referring to the
year, month, and day of the detection). The objects that produced the
GW150914 were a pair of stellar mass black holes that orbited each other
and gradually moved closer and closer together over the course of
eons. The closer together they became, the faster they orbited around
each other and the stronger the gravitational waves produced. LIGO
detected the last 0.2 seconds of these stars orbiting until they became
so close they merged into a single black hole.<br />
<br />
While we
saw the death of this paired (binary) system, we didn't get to observe other parts of its life. <i>Where did these black holes come from?</i> To answer this
question, we need to apply what we know about stellar evolution. <br />
<br />
<br />
<b>STELLAR MASS BLACK HOLES ARE CORPSES</b><br />
<br />
There
are several classes of black holes, determined by their mass and how
they were formed: <a href="https://en.wikipedia.org/wiki/Stellar_black_hole">stellar mass black holes</a>, <a href="https://en.wikipedia.org/wiki/Intermediate-mass_black_hole">intermediate mass black holes</a>, and <a href="https://en.wikipedia.org/wiki/Supermassive_black_hole">supermassive black holes</a>. For stellar mass black holes, they
formed when the most massive of stars (more than 15-20 times the mass
of our Sun) run out of nuclear fuel and <a href="https://en.wikipedia.org/wiki/Gravitational_collapse">gravity takes over and collapses the star</a>. For smaller stars, this collapse stops when the pressure
from inside the atom (<a href="https://en.wikipedia.org/wiki/Degenerate_matter#Neutron_degeneracy">neutron pressure</a>) equals the pressure from the
gravitational collapse. But for these more massive stars, there is no
pressure that can stop the collapse and a black hole is formed. It is
in this way stellar mass black holes are the corpses of the most
massive stars (but these kinds of black holes are among the least
massive). <u>The newly merged GW150914 black hole now holds the record for the largest stellar mass black hole known.</u><br />
<br />
There are several theories about how this
happens... Sometimes this collapse is accompanied by an explosion called
a <a href="https://en.wikipedia.org/wiki/Hypernova">hypernova</a> and is believed to be the source for a kind of <a href="https://en.wikipedia.org/wiki/Gamma-ray_burst">gamma-ray burst</a>. Sometimes the gravity of the collapsing star is so great that
all of the matter and light gets sucked into it even if there was a
hypernova-like explosion. <br />
<br />
<br />
<b>THE EVOLUTION OF THE GW150914 SYSTEM</b><br />
<br />
<i>But
how did two stellar mass black holes come to be paired together? </i> A likely explanation is that they also lived their lives together as a
<a href="https://en.wikipedia.org/wiki/Binary_star">binary star system</a>. This is very common as it is estimated that about 1 out
of 3 stars are in systems of 2 or more stars. This binary system would
likely have formed together and lived their entire lives paired. The
more massive of the 2 stars would have died first since <a href="https://en.wikipedia.org/wiki/Stellar_evolution">the more massive the star, the faster it burns through its fuel</a>. Once the nuclear fuel
ran out, the more massive star collapsed into a black hole making the system a star/black
hole system. Eventually, the second star would run out of fuel and
collapse into a black hole as well making our stellar black hole binary
system. These black holes would orbit for eons before they
were close enough to merge and produce the gravitational waves LIGO
detected.<br />
<br />
In a recent paper (see reference below or read it <a href="http://arxiv.org/abs/1602.04531">here</a>),
simulations of millions of stars with different material compositions
(specifically <a href="https://en.wikipedia.org/wiki/Metallicity">metalicity</a> which, to an astronomer, is anything that isn't
hydrogen or helium; the Sun is 2% 'metal') were simulated and some produced similar outcomes to
what we observed. What was found was that there were similar
characteristics for the stars the went on to resemble the GW150914
binary system and this gives us estimates on the time needed for each stage in the system's evolution from birth to the gravitational-wave-generating merger.<br />
<br />
The two stars were born about 2 billion
years after the Big Bang and were each somewhere between 40 to 100 times
the mass of our Sun. These low metalicity stars (only about 0.06% 'metal') orbit each other as stars for about 4
million years until the more massive one collapses into a black hole.
The now star-black hole system orbit each other for another 1.5 million
years until the other star collapses into a black hole. Both of these
stars were massive enough that there wouldn't have been a hypernova-like
explosion for either of them; any material ejected would have fallen
back into the black hole. Our new black hole binary system, which is
just the corpses of once very massive stars, now go on to orbit each
other for over 10 billion years - that is 1000 times longer than the
either star was a alive. At the end of that time, they merge and produce the gravitational waves that LIGO detected 1.3 billion years later when they arrived at Earth.<br />
<br />
<br />
<b>WHAT WILL HAPPEN NOW?</b><br />
<br />
The short answer: nothing. This new single black hole is spinning (it is the first detection of a <a href="https://en.wikipedia.org/wiki/Kerr_metric">Kerr rotating black hole</a>) but its shape and center of mass are not moving in a way that will ever produce gravitational waves again. Gravitational waves are also the only way this system would ever have been detected since there wasn't any matter (like dust or gas) to fall into the black holes and generate X-rays. We will never be able to observe this black hole again.<br />
<br />
Of course, there are extremely unlikely events like another black hole flying by and crashing into it... That may make new gravitational waves for us to see (but I wouldn't hold my breath).<br />
<br />
<br />
<b>Reference:</b><br />
<br />
K. Belczynski, D. Holz, T. Bulik, R. O'Shaughnessy, "The origin and evolution of LIGO's first gravitational-wave source" <a href="http://arxiv.org/abs/1602.04531">arXive e-Print: 1602.04531</a> (2016).<br />
<br />stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comLIGO Livingston Observatory30.5630717 -90.77311559999998330.5630182 -90.773194599999982 30.563125199999998 -90.773036599999983tag:blogger.com,1999:blog-4167914549123471212.post-14711481346626764492016-02-11T10:40:00.000-05:002016-06-15T11:58:38.966-04:00LIGO Makes the First Direct Detection of Gravitational WavesOn morning of <span style="color: #38761d;"><b>14 September 2015</b></span> at almost <span style="color: #38761d;"><b>4:51 am in Louisiana</b></span> (09:50:45 UTC) the LIGO detectors in Livingston, LA and Hanford, WA detected a <a href="http://stuver.blogspot.com/2012/05/q-what-is-gravitational-wave.html">gravitational-wave</a> signal we've labeled <span style="color: #38761d;"><b>GW150914</b></span> (based on the date). The online (near real-time) data analyses alerted scientists about 3 minutes later that there was something of substantial interest in the data. While vetting this signal (that only lasted about a half of a second) took a substantial amount of time, it opened the new field of <a href="https://en.wikipedia.org/wiki/Gravitational-wave_astronomy">gravitational-wave astronomy</a>. We had not only made the <span style="color: #38761d;"><b>first direct detection of gravitational waves</b></span> but we also made the <span style="color: #38761d;"><b>first direct detection of a black hole binary (pair) system</b></span> and proved that these kinds of systems really do exist (it was contentious because the formation of one of the <a href="https://en.wikipedia.org/wiki/Stellar_black_hole">black holes</a> was expected to have destroyed the star that would have made its partner).<br />
<br />
At the time of the posting of this blog, the press conference making the announcement is going on and I am working the satellite event being held at the Livingston Observatory. I will be sure to update this post with the link to the recording or the announcement later (update: see the bottom of this post). There is too much to talk about in just this post, so <span style="color: #38761d;"><b>I am going to keep this to the basics: <u>what did we see</u> and <u>what does it mean</u>?</b></span> I will be doing a series of posts about what we did to make sure that this is a real gravitational wave, the astrophysics of the source, how we detected it, the creation of black holes and why finding a pair like we did is important to astronomy.<br />
<br />
Update: Read the Physical Review Letters journal article <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102">here</a>. <br />
<br />
<br />
<b><span style="font-size: large;">THE SIGNAL</span></b><br />
<br />
This gravitational-wave detection was seen as a common signal between the two LIGO sites:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://3.bp.blogspot.com/-8gGzjC-JhVs/VrrDRusclcI/AAAAAAAABzU/YraqMUN6zmY/s1600/Fig1_Split_v17_top3_standalone.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="209" src="https://3.bp.blogspot.com/-8gGzjC-JhVs/VrrDRusclcI/AAAAAAAABzU/YraqMUN6zmY/s320/Fig1_Split_v17_top3_standalone.png" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">This image shows the data (top row), signal (middle row), and what's left over after the signal is subtracted from the data (bottom row). Detailed discussion on each image is provided below.</td></tr>
</tbody></table>
<span id="goog_626745609"></span><span id="goog_626745610"></span><span id="goog_293979046"></span><span id="goog_293979047"></span><br />
What you see here is a series of images (above and in detail below) that picks apart the signal that was detected. In the left column is information focusing on the <span style="color: red;">Hanford Observatory</span> and on the right the <span style="color: #3d85c6;">Livingston Observatory</span>.<br />
<br />
<b>TOP ROW:</b><br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-GVUU2aAttVQ/VrrM5Sp-e-I/AAAAAAAABzo/Gw-ElWEfNCY/s1600/top.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="179" src="https://2.bp.blogspot.com/-GVUU2aAttVQ/VrrM5Sp-e-I/AAAAAAAABzo/Gw-ElWEfNCY/s400/top.png" width="500" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The vertical (Y-axis) units are strain with a scale of 10<sup>-21</sup>.</td></tr>
</tbody></table>
<br />
In the top row is the signal that was seen. However, this is not the raw data as it was collected. What you see here is data that has been filtered to 1) reduce noise and 2) to include only <a href="https://en.wikipedia.org/wiki/Frequency">frequency</a> components that are around the frequency range of the signal itself. The <span style="color: red;">red graph on the left is the signal as seen at Hanford</span> and on the <span style="color: #3d85c6;">left the blue trace is as seen at Livingston</span>. For comparison, the light red line under the blue Livingston line is the Hanford signal that has been shifted in time to account for the travel time between detectors and flipped (multiplied by -1) to match the orientation of the arms (the arms of each site have a opposite orientation compared to each other so the positive signal in one detector will be negative in the other). The common signal can be seen with the noise in this comparison.<br />
<br />
<b>MIDDLE ROW:</b><br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-o_4U-x_yviw/VrrNO5lIfuI/AAAAAAAABzs/jROiaXNQ8-k/s1600/middle.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="179" src="https://2.bp.blogspot.com/-o_4U-x_yviw/VrrNO5lIfuI/AAAAAAAABzs/jROiaXNQ8-k/s400/middle.png" width="500" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The vertical (Y-axis) units are strain with a scale of 10<sup>-21</sup>.</td></tr>
</tbody></table>
<br />
These plots compare the signal predicted by <a href="https://en.wikipedia.org/wiki/Numerical_relativity">numerical relativity</a> (which are results of computer simulations where the predictions of <a href="https://en.wikipedia.org/wiki/General_relativity">general relativity</a> cannot be solved by in explicit mathematical expressions) for a <span style="color: #38761d;"><b>pair of black holes with one mass 36 times the mass of our Sun and the other 29 times</b></span>. (The <span style="color: red;">red line in the left plot for Hanford</span> and the <span style="color: #3d85c6;">blue line on the right for Livingston</span>.) Beneath each of these lines are grey shadowed areas that show the signal as detected from actual LIGO data with two different independent data analysis methods (wavelet and template). Here again, we can see that the predictions and observations match well.<br />
<br />
<b>BOTTOM ROW:</b><br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-411sMmrXcGc/VrrNTGzb1qI/AAAAAAAABzw/_3rt4SPcftE/s1600/bottom.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="115" src="https://4.bp.blogspot.com/-411sMmrXcGc/VrrNTGzb1qI/AAAAAAAABzw/_3rt4SPcftE/s400/bottom.png" width="500" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The vertical (Y-axis) units are strain with a scale of 10<sup>-21</sup>.</td></tr>
</tbody></table>
<br />
These are plots of residual signals which are the noise that this left behind when the gravitational-wave signal is removed. Seeing that there is no pattern left in these plots supports that what was seen was a real common signal - a real gravitational wave (this is <a href="https://en.wikipedia.org/wiki/Necessity_and_sufficiency">necessary</a> for a gravitational wave detection but not <a href="https://en.wikipedia.org/wiki/Necessity_and_sufficiency">sufficient</a> - the extra investigations performed will be the subject of a future post).<br />
<br />
<br />
<span style="font-size: large;"><b>THE SPECTROGRAM</b></span><br />
<br />
A powerful tool in signal analysis is breaking up a signal into its frequency components in a graph called a <a href="https://en.wikipedia.org/wiki/Spectrogram">spectrogram</a>. It allows us to see how much of a signal is made up different frequencies at different times. If you can hear, then you do this everyday. It is how you are able to pick apart the sound of a tuba from the sound of a flute when you listen to a symphony. Both are playing at the same time, but you don't confuse their sounds as coming from anything else.<br />
<br />
Below is the spectrogram of this gravitational wave detection:<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-_tUPaQ34xyY/VrrRR6ltl4I/AAAAAAAAB0E/p4GFq0tESKI/s1600/Fig1_Split_v17_bottom_standalone.png" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="156" src="https://1.bp.blogspot.com/-_tUPaQ34xyY/VrrRR6ltl4I/AAAAAAAAB0E/p4GFq0tESKI/s400/Fig1_Split_v17_bottom_standalone.png" width="500" /></a></div>
<br />
The horizontal (X-axis) is the progression of time (like above) and the vertical (Y-axis) is showing the contribution of each possible frequency. The more yellow at a frequency, the stronger that frequency's contribution to the signal at that time. Our gravitational wave starts at a low frequency (about 35 Hz) and increases to higher frequency (about 250 Hz) near the end of the signal. This is similar to a signal a slide whistle increasing tone would produce. <br />
<br />
<br />
<span style="font-size: large;"><b>WHAT WOULD THIS SOUND LIKE?</b></span><br />
<br />
As I've mentioned in <a href="http://stuver.blogspot.com/2012/06/what-do-gravitational-waves-sound-like.html">a previous post</a>, the frequencies of gravitational waves that LIGO is sensitive to would be audible if they were sound waves (which they aren't). Because of this, we can make them into sound waves by putting the signal through a speaker. So we did!<br />
<br />
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<br />
Because the starting frequency of the gravitational wave is very low, it is difficult to hear. The frequency is audible, but at that low of a frequency we tend to feel the sound vibration more than we hear it. So unless you have a truly great subwoofer, you will probably only hear the end "whoop" of the signal. In order to make the entire signal more audible, we shifted all of the frequencies up in the above sound up so you can hear the whole thing. This is not unlike the <a href="https://en.wikipedia.org/wiki/False_color">false-color</a> images made in astronomy for light that our eyes cannot see.<br />
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<div class="separator" style="clear: both; text-align: center;">
<iframe allowfullscreen='allowfullscreen' webkitallowfullscreen='webkitallowfullscreen' mozallowfullscreen='mozallowfullscreen' width='320' height='266' src='https://www.blogger.com/video.g?token=AD6v5dxQy_1RAdQOJng_9I9IDF_2eua3P2w-BBrKLRREto7wZEwCoYzZ3cuiMJG-UI8h-JU1bEQe9Wab9_hQaWF2wQ' class='b-hbp-video b-uploaded' frameborder='0'></iframe></div>
<br />
<br />
Now that you've heard the detected gravitational wave, you can see that when the tone of it becomes higher toward the end of the signal, the frequency in the spectrogram also goes up.<br />
<br />
<br />
<span style="font-size: large;"><b>WHERE DID THE SIGNAL COME FROM?</b></span><br />
<br />
Because the two LIGO detectors were the only detectors operating at the time of the event (<a href="http://www.virgo-gw.eu/">Virgo</a> in Italy is finishing their advanced detector upgrades and <a href="http://gwcenter.icrr.u-tokyo.ac.jp/en/">KAGRA</a> in Japan is under construction with similar advanced instrumentation) it isn't easy to state precisely where the signal came from. We can narrow it down to an area on the sky based on how long it took the gravitational wave to travel between the two LIGO detectors, and other factors like the strength of the signal in each detector (there is a slightly different response for each detector for different sky locations). The most probable location is in the <span style="color: #38761d;">southern hemisphere around the constellations Volans and Carina</span>:<br />
<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-RTo9Ydx5t6M/Vrrh-B-MoII/AAAAAAAAB0Y/cgQur6lPwXs/s1600/skylocation_galaxy_preview.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="250" src="https://1.bp.blogspot.com/-RTo9Ydx5t6M/Vrrh-B-MoII/AAAAAAAAB0Y/cgQur6lPwXs/s400/skylocation_galaxy_preview.jpg" width="500" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b>The colored area on this map shows the most probable source of the detected gravitational wave where red is more likely than purple. The location is shown against a map of the night sky centered on the Milky Way galaxy with constellations outlined. </b><br />
[Credits: NASA Deep Star Maps (Visualization Credits, Ernie Wright (USRA): Lead
Animator, Tom Bridgman (GST): Animator) by NASA/Goddard Space Flight
Center Scientific Visualization Studio with constellation figures based
on those developed for the IAU by Alan MacRobert of Sky and Telescope
magazine (Roger Sinnott and Rick Fienberg), and the source location
based on Gravoscope screen grabs (LIGO & Nick Risinger, <a href="http://skysurvey.org/" target="_blank">skysurvey.org</a>), all in galactic coordinates. Composition by University of Florida / S. Barke.]</td></tr>
</tbody></table>
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<br />
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<span style="font-size: large;"><b><span style="font-size: small;"> </span> </b></span><br />
<span style="font-size: large;"><b>WHAT MADE THIS GRAVITATIONAL WAVE?</b></span><br />
<br />
Two different data analysis methods that look at the data in fundamentally different ways not only detected this event, but provided the same results for what the source of it was. This gravitational wave was made by two <a href="https://en.wikipedia.org/wiki/Stellar_black_hole">stellar mass black holes</a> (these are the remnants of extremely massive stars that have expended their fuel and collapsed under their own gravity). As quoted above, their masses were about 29 and 36 times the <a href="https://en.wikipedia.org/wiki/Solar_mass">mass of our Sun</a>. They orbited around each other for hundreds of thousands to millions of years before they come close enough together to start orbiting very quickly (much like an ice skater spins faster as they draw their arms into themselves). LIGO was only sensitive to the very end of this process right before the two black holes merged into one black hole. At the end, the stars had a relative velocity of about 1.8x10<sup>8</sup> m/s, or 60% the <a href="https://en.wikipedia.org/wiki/Speed_of_light">speed of light</a> (the universe's "speed limit"). Imagine that... Two black holes that were each the size of cities but each about 30 times as massive as our Sun whirling around each other at more than half the speed of light! The animation below shows what it may have looked like to see these black holes merge together. Note that since they are black holes, no light come from them directly but they do bend the light that is coming from behind them in a process called <a href="https://en.wikipedia.org/wiki/Gravitational_lens">gravitational lensing</a>:<br />
<br />
<div style="text-align: center;">
<iframe allowfullscreen='allowfullscreen' webkitallowfullscreen='webkitallowfullscreen' mozallowfullscreen='mozallowfullscreen' width='450' height='374' src='https://www.blogger.com/video.g?token=AD6v5dyEx3Dr9CgYbqcUPdGKR058LknYLe30axhzusRUZN1cCV-AbHlLeRiJmswB5_GoMqDI6-DV26dWCQ6eOx4wSA' class='b-hbp-video b-uploaded' frameborder='0'></iframe></div>
<br />
Based on how strong we know these gravitational waves were at their source as predicted by general relativity and how strong they were once they reached Earth, we estimate that this system is located about 1.3 billion light years (~410 Mpc) away. That distance is about 10% of the way to the edge of the <a href="https://en.wikipedia.org/wiki/Observable_universe">observable universe</a>! It also means that the gravitational waves we just detected have been traveling into the universe and toward us for 1.3 billion years. When these gravitational wave were created the Earth was in the <a href="https://en.wikipedia.org/wiki/Proterozoic">Proterozoic eon</a> of <a href="https://en.wikipedia.org/wiki/Precambrian">Precambrian time</a>, after when multicellular life developed but before animal life.<br />
<br />
<span style="font-size: large;"><b>PRESS CONFERENCE RECORDING</b></span><br />
<br />
<span style="font-size: large;"><span style="font-size: small;">Note: Fast forward to 26:30. It's just waiting before that. </span><b> </b></span><br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/aEPIwEJmZyE/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/aEPIwEJmZyE?feature=player_embedded" width="320"></iframe></div>
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<br />
<span style="font-size: large;"><span style="color: magenta;"><b>Next post: On the formation of stellar mass black hole and why this pair of them are interesting to astronomy...</b></span></span><br />
<br />stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.com19100 Ligo Rd, Livingston, LA 70754, USA30.562997199999991 -90.7742061999999815.0409626999999908 -132.08280019999998 56.085031699999988 -49.465612199999981tag:blogger.com,1999:blog-4167914549123471212.post-57789278117631234892015-11-04T23:36:00.001-05:002015-11-04T23:36:24.752-05:00How We Monitor Data Collection with Advanced LIGOThe first Advanced LIGO observing run (O1) started in mid-September and will end in mid-January. Today I want to tell you about how we collect our data. On the surface this is obvious: with computers and sensitive electronics. <b>But how do we keep the detector working so that we can collect data and how do we know that our data is good?</b><br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/--ZVfZ4lqQaQ/Vjknff9zQhI/AAAAAAAABqY/IERkQjdnU5k/s1600/2015-11-03%2B15.06.25.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="165" src="http://2.bp.blogspot.com/--ZVfZ4lqQaQ/Vjknff9zQhI/AAAAAAAABqY/IERkQjdnU5k/s400/2015-11-03%2B15.06.25.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The LIGO Livingston control room on 3 November 2015 (during O1).</td></tr>
</tbody></table>
<br />
<b>OPERATORS</b><br />
<br />
The most important step in collecting data is that the detector is working. This is the primary job responsibility of the roughly 10 operators who work at the site. There are 3 10-hour shifts a day, each one overlapping with the previous operator's shift by 2 hours so that the incoming operator can be brought up to speed on any issues that may be ongoing. Since O1 will last into mid-January, that means that there will be at least the operator in the control room every night, weekend, and holiday - even during Thanksgiving dinner, Christmas morning, and New Years at midnight! <br />
<br />
During their shift, they monitor various things like the power of the laser, local vibrations, and a multitude of other readings from all over the detector that tend to drift over time. This work is mainly to prevent a fault in one of the systems that would interrupt data collection. When everything is working the way it is supposed to, this part of their job can be boring - and we love boring days and nights. <br />
<br />
Excitement happens when we are no longer able to keep the light bouncing back and forth between the mirrors (we call this "breaking lock"). The operator's job now is to respond by discovering if the lock was lost due to an environmental issue we can't control (like an earthquake anywhere on the planet) or due to an detector issue. If there is a malfunction in the detector, the operator identifies what subsystem caused the problem and then uses their training to fix it and get the detector up and running again. Through my conversations with them, one of the harder parts of their job is identifying which part of the detector isn't working properly since there are so many subsystems that need to work all at the same time for us to be able to collect data.<br />
<br />
<b>SCIENTISTS</b><br />
<br />
During the Initial LIGO science runs, there were always 2 people in the control room: the operator and the "scimon" (short for science monitor). The scimon's job was to ensure the quality of the data that was being collected and give feedback to the operator. Scimons came from institutions across the country who would usually spend a week or two at the observatory before returning to their home. This meant that there were a lot of people passing though the observatory (which isn't bad) and by the time they really got comfortable in their job it was time for them to go home (this isn't good). <br />
<br />
We are doing the science monitoring differently for Advanced LIGO: we have longer-term (several months) visiting scientists (LSC Fellows) working on site to monitor the data as it is collected and we have data quality scientists (we call them "DQ Shifters") who remotely monitor the properties of the data for a period of 3-4 days.<br />
<br />
<b>SCIENTISTS: LSC FELLOWS</b><br />
<br />
These scientists are on-site to monitor the data as it is collected and they also each have a project related to improving the instrument. There is almost always a fellow on-site except for the earliest hours of the day (they are not as necessary as the operator and their instrument research is best done when other scientists are also around). The fellows work with the operators to identify subsystems that may be causing issues and they work to resolve them. Basically, these are the Advanced LIGO version of the scimon but with the benefit of having the visiting scientist being able to apply what they learn while on site.<br />
<br />
<b>SCIENTISTS: DQ SHIFTERS</b><br />
<br />
The DQ shifter is a scientist who monitors the quality of the data that has already been taken (within about a day or so). Sometimes, patterns only become evident after a significant amount of data has been collected. Because this work is not expected to have immediate feedback to the operators and fellows, this work can be done remotely. We have created automated web pages that have all the plots needed to look at how the different parts of the detector are working. There are about 40 or so of us (including me) who have been trained on how to interpret all of the graphs that appear on these pages and what specific things we should be watching for. We communicate with the fellows at the site we are monitoring on a daily basis so that they can use the feedback to improve the quality of the data. When our shift is done (we usually cover 3-4 days in a shift), we document our findings, report to the data quality group who specializes in studying collected data, and we enter an entry in the detector log with a summary of our shift.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-wk5aEUyJKq8/VjkoH2TJtjI/AAAAAAAABqg/3OpdAH7Ha0c/s1600/Nov2SEIsummary.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="233" src="http://3.bp.blogspot.com/-wk5aEUyJKq8/VjkoH2TJtjI/AAAAAAAABqg/3OpdAH7Ha0c/s400/Nov2SEIsummary.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Summary pages used by DQ Shifters to evaluate the quality of data already taken. These plots specifically show how the ground was moving in different frequency bands throughout the day on 2 November 2015.</td></tr>
</tbody></table>
<br />stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comLIGO Livingston, 19100 Ligo Rd, Livingston, LA 70754, USA30.562997199999991 -90.77420619999998130.50829619999999 -90.854887199999979 30.617698199999992 -90.693525199999982tag:blogger.com,1999:blog-4167914549123471212.post-23789709754533700072015-07-31T21:24:00.001-04:002015-08-04T22:06:17.745-04:00First Science Data With Advanced LIGO is Near!It has been a very exciting time for Advanced LIGO
recently. A few weeks ago we completed a test run of the instrument to
identify any remaining bugs in the instrument or other stability
issues. The commissioners (instrumental scientists who work on making LIGO
more sensitive) have been busy adjusting various settings in a
multitude of subsystems to increase our sensitivity to gravitational
waves. We are continuously learning more about how all of these
subsystems react to one another and to the environment. And learning is
never without its own pains. Some bugs have been bigger than others.
We've had to actually touch the new instrumentation - meaning we had to
seal off the chamber the part was in, let the air back in (since almost
all of the instrument is in a vacuum), fix it, close up the chamber, and
pump the air back out. This is rare but it has happened. Once the
instrument was performing well, that's when we decided to stop tinkering
with it and use it like we would if we were looking for gravitational
waves. More subtle issues in stability and other bugs will make
themselves apparent only after you use it the way it's meant to be used -
all the time.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-hb8kwjwjNz4/VbwhnoOliRI/AAAAAAAABg4/y-hsB8Q8cEU/s1600/PuttingLHOTogether.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="212" src="http://3.bp.blogspot.com/-hb8kwjwjNz4/VbwhnoOliRI/AAAAAAAABg4/y-hsB8Q8cEU/s320/PuttingLHOTogether.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Installing one of Advanced LIGO's seismic isolation platforms at the Hanford observatory in 2013.</td></tr>
</tbody></table>
<br />
<b>ENGINEERING RUNS </b><br />
<br />
These test runs are called engineering
runs. We abbreviate them ER followed by the number of the run. The
last one was called ER8. <a href="http://stuver.blogspot.com/2012/01/first-software-engineering-run-for.html">I've already talked about the first one (ER1)</a>
back when almost everything was being simulated since the installation
of the instruments was just getting off the ground. The purpose of
those early engineering runs was to test out the ability of our data
analysis systems to handle the large amount of data we will collect. As
parts of aLIGO
were installed, we replaced the simulated data from that component with
real data. ER8 was our first test of all of the instrument without
anything being simulated. While the purpose of this data is to test the
stability of the whole system and to find other small bugs, we are
still running all of our data analysis methods over the collected data.
We don't expect to find a gravitational wave in this data, but if we
have compelling reason to believe that we really did see something we
will certainly pursue it as a real detection. Don't get too excited,
though, since there are no indications that we collected a gravitational
wave.<br />
<br />
<b>OBSERVING RUNS </b><br />
<br />
What is really exciting is that we are preparing
to make that first detection. We don't really expect to detect a
gravitational wave with our first science data (which will be called O1 -
observation 1) with aLIGO but it is not as improbable as it was with Initial LIGO. We are talking about what we learned from the blind injection in our last iLIGO
data set (otherwise known as <a href="http://stuver.blogspot.com/2011/03/big-dog-in-envelope.html">the "Big Dog" event</a>) and what our detection validation should entail. We are talking about writing the
paper that we will publish announcing the first detection and its
details. We are even talking about how we will engage the public with
this announcement. Don't misunderstand me - we have not seen anything yet, but we are preparing ourselves for the possibility of detection.<br />
<br />
<b>DETECTION IS POSSIBLE... </b><br />
<br />
You
really don't have any idea how exciting this is especially for those of
us who have been around a while (I have been working on LIGO
since starting grad school in 1999 and I'm a youngster). I have been working on this
project that is so much bigger than myself since before we took our
first data with Initial LIGO.
I remember when the collaboration was a couple hundred scientists
(there are now almost 1000 of us). I remember when we analyzed our
first data and debated how to interpret our detection candidates when we
almost sure that everything we had was noise (i.e. garbage). Now we
are talking about confidently making a detection, and doing astronomy
with it. This is the dawn of a new age in astronomy and I'm proud to be
here to see it.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-5djnquXkbfw/TkV7zIrmPdI/AAAAAAAAAK0/BGrk27J6cbw/s1600/FOM1.png" style="margin-left: auto; margin-right: auto;"><img border="0" height="207" src="http://1.bp.blogspot.com/-5djnquXkbfw/TkV7zIrmPdI/AAAAAAAAAK0/BGrk27J6cbw/s320/FOM1.png" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Distance in parsecs (1 pc = 3.26 light years) Initial LIGO
was able to detect its standard source of 2 neutron stars orbiting each
other just before they merge into one body. (Read more <a href="http://stuver.blogspot.com/2011/08/q-what-waswill-be-detection-range-of.html">here</a>.) <br />
aLIGO wil be able to "see" up to 200 Mpc (about 650 million light years).</td></tr>
</tbody></table>
Remember, we don't expect a detection, but it is possible. To give you an idea of how possible, once we have aLIGO working at the sensitivity it was designed to work at, it will observe as much of the universe in several hours as Initial LIGO
did in an entire year. We won't be at design sensitivity for O1, but
we can already detect our standard source 4 times farther away than we
could on our best days with Initial LIGO.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-rILRheu_Dss/Vbwd1xtMzDI/AAAAAAAABgk/rgaa5YHYLb4/s1600/PMC_Smiley.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" height="319" src="http://1.bp.blogspot.com/-rILRheu_Dss/Vbwd1xtMzDI/AAAAAAAABgk/rgaa5YHYLb4/s320/PMC_Smiley.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">An
image of light that was filtered out of the laser before entering the
LIGO detector. Bend your neck to the right and you should be able to
see a smiley face. This is just a chance configuration and has no
significance, but we thought it was cool.</td></tr>
</tbody></table>
stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comtag:blogger.com,1999:blog-4167914549123471212.post-73265622745920188882015-06-01T14:11:00.001-04:002015-06-01T15:16:51.367-04:00Advanced LIGO is Here!I've been away from all of you for a little over a year due to many factors including teaching new courses, starting new research projects, and more than a few personal reasons. However, I wanted to let all of you know about the status of Advanced LIGO (spoiler: it's done) and that I will be back to posting on this blog on a regular basis.<br />
<br />
<b>ADVANCED LIGO</b><br />
<br />
On 20 October 2010, Initial LIGO (iLIGO) recorded its last bits of science data [<a href="http://stuver.blogspot.com/2010/10/initial-ligo-is-dead-long-live-advanced.html">read the blog post here</a>]. At that time, we were taking some of the most sensitive gravitational wave data and we thought we may have recorded a real gravitational wave (it was a fake signal purposefully placed in the data to test our ability to find real gravitational waves, but we didn't know that at the time [<a href="http://stuver.blogspot.com/2011/03/big-dog-in-envelope.html">you can read all about it here</a>]). The metaphorical "keys" to the detector were transferred from operations to the aLIGO installation team.<br />
<br />
In the nearly 5 years since iLIGO, we've removed all of the old instrumentation, much of which had been designed 15 years ago (remember what cell phones looked like back then? - we've come a long way) and replaced it with newly redesigned instruments. You won't notice anything different by flying over LIGO (there was not real estate expansion) but we gutted at very intricate and technical instrument and replaced it with more sophisticated hardware. The details on the upgrades could make a whole series of blog posts, but a few of them included improved seismic (ground vibration) isolation, better ways to hang our mirrors like pendula, a more powerful laser, more massive mirror, better coatings on the mirrors, and new ways to reuse laser light to increase the laser power in the the arms. All of this will combine to make aLIGO over 10 times as sensitive as it was before allowing us to observe 1000 times more of the universe than with the original observations we made.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-2VstR0y4eIw/TL-j1gBYkAI/AAAAAAAAADw/2aMXHx6mr8k/s1600/aLIGO.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="272" src="http://1.bp.blogspot.com/-2VstR0y4eIw/TL-j1gBYkAI/AAAAAAAAADw/2aMXHx6mr8k/s320/aLIGO.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The illustration above shows the anticipated "reach" of Advanced LIGO (the purple sphere) compared to Initial LIGO (the orange sphere). Each small dot in the figure represents a galaxy. Since the volume of space that the instrument can see grows as the cube of the distance, this means that the event rates will be more than 1,000 times greater. Advanced LIGO will equal the 1-yr integrated observation time of Initial LIGO in roughly 3 hours. (Galaxy map credit: R. Powell, <a href="http://www.atlasoftheuniverse.com/">www.atlasoftheuniverse.com</a>.)
</td></tr>
</tbody></table>
<br />
On 19 May 2015, aLIGO was dedicated at the Hanford, WA observatory (since I am at the Livingston, LA site and generally unimportant, I missed out). The "keys" are now back with the operations team at both sites (the Livingston site was scheduled to be 'done' before Hanford and has been 'working' for several months now). Why did I put <i>done </i>and <i>working</i> in quote in my parenthetical comment? Well, now is the time for commissioning. The detector can turn on and operate as in <a href="http://www.ligo.org/science/GW-IFO.php">interferometer</a> but all of the new components aren't yet optimized to work together resulting in the detector being less sensitive than it was designed to be. The work that is currently gong in with the detector is commissioning work that seeks to work on individual subsystems so that the detector works better as a whole. In short, this is our version of tuning up our car.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-I2qWdcOemQs/VWjgqqd6hJI/AAAAAAAABUM/g3Emue7Xsz4/s1600/11026081_792445000862958_4321178199993446151_n.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="240" src="http://1.bp.blogspot.com/-I2qWdcOemQs/VWjgqqd6hJI/AAAAAAAABUM/g3Emue7Xsz4/s320/11026081_792445000862958_4321178199993446151_n.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Break time at the Advanced LIGO dedication at the LIGO Hanford Observatory on 19 May 2015. [Source: <a href="https://www.facebook.com/LigoScientificCollaboration">LIGO Scientific Collaboration's Facebook page</a>]</td></tr>
</tbody></table>
<br />
Even though neither detector is working at the sensitivity it was designed to, we are regularly setting sensitivity records when we do turn on the detector to test the commissioning work. One of the ways we measure our sensitivity is to determine the farthest distance away a standard source of gravitational waves could be for us to just be able to detect it. The standard source we use is two neutron stars orbiting each other and merging into one. (We picked this because it is a simple system were we can predict how big the gravitational waves will be and what shape the waves will have.) We call this the inspiral range. Below is the insprial range for each aLIGO detector (Livingston is the blue squares line and Hanford is the red dots line) given the number of days since the aLIGO installation was declared complete (there are more data points for Livingston since we were scheduled to be done a little before Hanford).<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-vbFrqWKcoAs/VWjkR2TQzhI/AAAAAAAABUs/vq90crUSCxc/s1600/Screenshot%2B2015-05-29%2B17.12.13.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="250" src="http://2.bp.blogspot.com/-vbFrqWKcoAs/VWjkR2TQzhI/AAAAAAAABUs/vq90crUSCxc/s400/Screenshot%2B2015-05-29%2B17.12.13.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The distance into the universe we would be able to detect a
gravitational wave from our reference source of two neutron stars orbiting each other and merging into one. [Source: Talk given by David Shoemaker at the aLIGO Dedication on 19 May 2015]</td></tr>
</tbody></table>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
Our best data with iLIGO was able to detect out to about 20 Mpc (a little over 65 million light years away). Currently, the Livingston's inspiral range is at 65 Mpc (212 million light years) and Hanford's is at 57 Mpc (almost 186 million light years). So, even though we are still commissioning the detectors, we are already gathering the most sensitive gravitational-wave data ever!<br />
<br />
<br />
<b>IN MEMORY:</b><br />
<br />
<div style="text-align: center;">
<b>Cristina Torres</b></div>
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="http://4.bp.blogspot.com/-HvKFeFk1dZA/VWjn6LBN_gI/AAAAAAAABU4/wDUW_8bG4DU/s1600/2012-07-27%2B17.42.56.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="320" src="http://4.bp.blogspot.com/-HvKFeFk1dZA/VWjn6LBN_gI/AAAAAAAABU4/wDUW_8bG4DU/s320/2012-07-27%2B17.42.56.jpg" width="191" /></a></div>
I lost a very good friend a few moths ago. Cristina and I were both postdocs at LIGO Livingston until 2012 when she took a position at the <a href="http://www.phys.utb.edu/people/torres.php">University of Texas at Brownsville</a> as a professor. We shared a passion for engaging others in our science, but she always had an openness to others that I have admired. She was a better friend to me than I ever was to her, but if she was here to read this she would argue with me since she did exactly that in one of our last emails. <br />
<br />
The last time I saw her in person was when I was at UT Brownsville earlier this year to speak about work/life balance, which I don't <i>really </i>have figured out, at a regional <a href="http://www.aps.org/programs/women/workshops/cuwip.cfm">Conference for Undergraduate Women in Physics</a> (there is a beautiful tribute to her at the bottom of this page). She was so stressed since much of the local organization and logistics was on her shoulders but the meeting went very well! If I had any idea that I wouldn't be seeing her again, I would have made more of an effort to spend time with her (instead of just trying to stay out of her hair).<br />
<br />
This is a picture of Cristina with a prototype of the new mirror suspension system at LIGO Livingston in 2012. We use this display to show visitors some of the upgrades that they aren't able to see inside of aLIGO. <br />
<br />
Until again, Cristina... stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comLIGO Livingston, 19100 Ligo Road, Livingston, LA 70754, USA30.562997199999991 -90.77420619999998130.508297199999991 -90.854887199999979 30.617697199999991 -90.693525199999982tag:blogger.com,1999:blog-4167914549123471212.post-31295753134963269862014-03-21T18:03:00.000-04:002015-06-01T14:33:29.443-04:00Gravitational Waves Seen in the Polarization of Light From the Big Bang<b>THE COSMIC MICROWAVE BACKGROUND</b><br />
<br />
The oldest light we can see in the Universe is called the <a href="http://en.wikipedia.org/wiki/CMB">cosmic microwave background (CMB)</a> and it is the relic light from the <a href="http://en.wikipedia.org/wiki/Big_Bang">Big Bang</a>. While this light is old, it isn't quite as old as our Universe. Before an event called <a href="http://en.wikipedia.org/wiki/Recombination_%28cosmology%29">recombination</a>, the Universe was not transparent to light, so the light couldn't propagate very far before being absorbed. Recombination happened about 380,000 years after the Big Bang and the light from this time is what we observe in the CMB.<br />
<br />
Everywhere we look on the sky, the frequency of this microwave light is very nearly the same. Since heat can be transmitted through radiation (such as microwaves), we can characterize this light to have a temperature of about 3 K (or about 3 <sup>o</sup>C or 5.4 <sup>o</sup>F above absolute zero - the coldest anything in the Universe can be). Why this temperature is the same everywhere on the sky doesn't immediately make sense since the heat hasn't had enough time to be transferred across the Universe.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-4A_TK_n5NfU/UyvdOs3HHDI/AAAAAAAAA70/p_A4hU2AWak/s1600/WMAP.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://3.bp.blogspot.com/-4A_TK_n5NfU/UyvdOs3HHDI/AAAAAAAAA70/p_A4hU2AWak/s1600/WMAP.png" height="160" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The slight variations in the CMB temperature from opposite sides of the sky as measured by 9 years of data from the <a href="http://en.wikipedia.org/wiki/WMAP">WMAP</a> mission. The fluctuation in the CMB temperature is measured to be <code>±</code> 0.0002 <sup>o</sup>C (0.00036 <sup>o</sup>F). [Source: <a href="http://en.wikipedia.org/wiki/File:Ilc_9yr_moll4096.png">Wikipedia</a>]<code><br /></code></td></tr>
</tbody></table>
<br />
The CMB is almost 14 billion light years away from us. This is approximately the age of the Universe. But there is no way for light to transfer heat from one side of the Universe (14 billion light years from us) and reach the other side (14 billion light years away from us in the opposite direction) since this would take about 28 billion years of travel time or <b>twice the age of the Universe</b>! So there is no way that these widely separated parts of the Universe should have the same temperature <i>if</i> the Universe has expanded in a continuous way since the Big Bang.<br />
<br />
To explain why the CMB is essentially in thermal equilibrium in every part of the Universe, something extraordinary needed to happen...<br />
<br />
<br />
<b>INFLATION </b><br />
<br />
Almost immediately after the <span class="il">Big</span> <span class="il">Bang</span>, it is believed that the Universe entered a period of extremely rapid expansion called <a href="http://en.wikipedia.org/wiki/Inflation_%28cosmology%29">inflation</a>. This began at about 10<sup>-35</sup> seconds after the <span class="il">Big</span> <span class="il">Bang</span> and the Universe proceeded to expand its volume by about 80 orders of magnitude (that's a 1 followed by 80 zeroes) in a fraction of a second. During this time, gravitational<span class="il"> waves</span> would have originally been produced on a quantum mechanical scale and then blown up to cosmological scales during inflation. The gravitational <span class="il">waves</span> from the <span class="il">Big</span> <span class="il">Bang</span> are exactly these fluctuations in space-time that are still vibrating from the period of inflation. (The wavelength now is its original wavelength, i.e. about 1% of the size of the Universe as it was then, stretched by the amount the Universe has expanded since then.)<br />
<br />
<br />
<b>EVIDENCE OF GRAVITATIONAL WAVES IN THE CMB</b><br />
<br />
Since gravitational waves were able to propagate through the early Universe long before light was, it is expected that there is evidence of these gravitational waves contained within the CMB. We expect to see this in a special kind of polarization of the CMB (where polarization refers to the rotational orientation of the light waves). There should be 2 kinds of polarization in the CMB, E-mode and B-mode.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-kE1U30SJGCQ/UyvWVMGa_II/AAAAAAAAA7Q/mZPubR74K2A/s1600/HistoryOfUniverse-BICEP2-20140317.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://3.bp.blogspot.com/-kE1U30SJGCQ/UyvWVMGa_II/AAAAAAAAA7Q/mZPubR74K2A/s1600/HistoryOfUniverse-BICEP2-20140317.png" height="247" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">A graphical history of the Universe showing when gravitational waves would have been created and how they affect matter along with density waves and their affect. The effects that gravitational waves have on mattert cause B-mode polarization in the CMB while density waves are the primary contributors of E-mode polarization. [Source: <a href="http://en.wikipedia.org/wiki/File:HistoryOfUniverse-BICEP2-20140317.png">Wikipedia</a>]</td></tr>
</tbody></table>
<br />
E-mode polarization means that the orientation of the polarization should not change as you move in a straight line. <a href="http://en.wikipedia.org/wiki/B-modes">B-mode polarization</a> means that the rotation of the polarization changes or "curls" around itself. The E and B in these mode names refer to how electric (E) and magnetic (B) fields behave: a single charge will have an electric field pointing radially away from a single change while a magnet always have 2 poles causing the magnetic field to always curl back to the magnet. The E-mode polarization in the CMB provides information about the fluctuation of density in the early Universe. Because <a href="http://stuver.blogspot.com/2012/06/q-what-would-gravitational-wave-feel.html">gravitational waves alternate, compressing space in one direction and expanding it in the orthogonal (at a right angle) direction</a>, they caused the "curling" B-mode polarization.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-qurPO6PAmJc/Uyvax_k53rI/AAAAAAAAA7o/z4xIylkzY6U/s1600/BICEP2EmodeBmode.jpeg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://1.bp.blogspot.com/-qurPO6PAmJc/Uyvax_k53rI/AAAAAAAAA7o/z4xIylkzY6U/s1600/BICEP2EmodeBmode.jpeg" height="239" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Graphical illustration of the polarization patterns for E-modes and B-modes. Note that B-mode patterns can be characterized by "rotating" clockwise or counter-clockwise while the E-modes cannot. [Source: <a href="http://www.cfa.harvard.edu/pao/Bicep2_news_con.mp4">Press conference</a> screen grab] </td></tr>
</tbody></table>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
An experiment called <a href="http://en.wikipedia.org/wiki/BICEP_and_Keck_Array">BICEP2</a> (Background Imaging of Cosmic Extragalactic Polarization) announced to the world a few days before this post (17 March 2014) that they did indeed detect the B-mode polarization in the CMB. The results are cataloged <a href="http://bicepkeck.org/">here</a>.<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="http://2.bp.blogspot.com/-rWq_iEg9qQ0/Uyveiv4GPbI/AAAAAAAAA8E/ElItsu20P0A/s1600/BICEP2Bmode.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://2.bp.blogspot.com/-rWq_iEg9qQ0/Uyveiv4GPbI/AAAAAAAAA8E/ElItsu20P0A/s1600/BICEP2Bmode.jpg" height="182" width="320" /></a></div>
<br />
The above image is the polarization of different points in the sky they observed from the South Pole. The red colored areas are where the B-modes can be classified as clockwise and the blue colored areas are where they can be classified as counter-clockwise.<br />
<br />
<div style="text-align: center;">
<span style="color: red;"><b>THIS IS THE IMPRINT OF GRAVITATIONAL WAVES FROM THE PERIOD OF INFLATION!</b></span></div>
<br />
Any time scientists think they found something that they wanted to find, we immediately set to trying to disprove what we found. (This is <a href="http://stuver.blogspot.com/2011/03/big-dog-in-envelope.html">discussed on this blog</a> in regard to LIGO with the blind injections known as "<a href="http://stuver.blogspot.com/2011/03/big-dog-in-envelope.html">The Big Dog</a>".) After thorough vetting and analysis of this work, it has been determined that the chance of this B-mode signal has a chance of 1 in 3.5 million of being a false detection. <br />
<br />
<br />
<b>WHAT THIS MEANS FOR LIGO AND SIMILAR DETECTORS</b><br />
<br />
This discovery of the imprint of gravitational waves on the CMB further hints at the promise that gravitational-wave astronomy with detectors like LIGO will have in the future. Their discovery in no way diminishes the potential of LIGO and gravitational-wave astronomy - instead it increases its promise.<br />
<br />
LIGO seeks to work like a gravitational-wave radio and record the gravitational-wave signals directly. (This analogy is discussed in more depth on this blog <a href="http://stuver.blogspot.com/2012/06/what-do-gravitational-waves-sound-like.html">here</a>.) For this analogy, the information about what made the gravitational wave is the music being carried on the radio wave (the gravitational wave in this analogy). In this sense, LIGO will be making a distinctly different kind of detection than BICEP2 did. We will be directly recording a gravitational wave as it passes by Earth and BICEP2 detected the imprint of gravitational waves on the CMB.<br />
<br />
Also, LIGO looks for a wider range of gravitational waves. While we also look for the relic gravitational waves from the Big Bang which we call <a href="http://www.ligo.org/science/GW-Stochastic.php">stochastic</a> gravitational waves, we search for three other kinds: <a href="http://www.ligo.org/science/GW-Continuous.php">continuous</a>, <a href="http://www.ligo.org/science/GW-Inspiral.php">inspiral</a>, and <a href="http://www.ligo.org/science/GW-Burst.php">burst</a>. (These are described in more detail on this blog <a href="http://stuver.blogspot.com/2012/06/what-do-gravitational-waves-sound-like.html">here</a>.) This broad range of gravitational waves that detectors like LIGO will be able to "see" will allow gravitational waves to tell their own story of how they were made; perhaps from the collapse of a star into a black hole or the merging of two stars into one, or the echoes of the birth of the Universe. We will not be seeing the evidence of gravitational waves that is imprinted onto light, but collecting information from the gravitational waves themselves.<br />
<br />
As a side note: <a href="http://en.wikipedia.org/wiki/Kip_Thorne">Kip Thorne</a>, a physicist who has pioneered work in general relativity and gravitational waves, made a prediction in 2006 of what detections will be made with gravitational waves in the next 50 years:<br />
<blockquote class="tr_bq">
"Over the next 50 years, gravitational waves from the big bang will be
detected, first indirectly by the imprint they leave on the cosmic
microwave radiation and then directly, by space-based gravitational wave
observatories."</blockquote>
You can read the rest of his prediction on <a href="http://www.newscientist.com/article/dn10563-kip-thorne-forecasts-the-future.html#.UyqCSzzt4T5">NewScientist.com</a>.<br />
<br />
Read LIGO's <a href="http://www.ligo.org/news/bicep-result.php">official congratulatory statement on the BICEP2 results to the ligo.org web page</a>.<br />
<br />
<b>WHAT THIS MEANS FOR COSMOLOGY</b><br />
<br />
The BICEP2 results do much more than suggest or support that inflation happened: it gives us some information about what happened during inflation. The strength of the signals observed here informs us on the energy involved in inflation. The ratio of the strength of the E-modes to the B-modes (a value referred to as r and measured here to be r = 0.2) is proportional to the energy density of the Universe at the time of inflation and this is consistent with energies needed in some of the <a href="http://en.wikipedia.org/wiki/Grand_Unified_Theory">grand unified theories (GUTs)</a> (this is where the <a href="http://en.wikipedia.org/wiki/Strong_interaction">strong</a>, <a href="http://en.wikipedia.org/wiki/Weak_interaction">weak</a>, and <a href="http://en.wikipedia.org/wiki/Electromagnetism">electromagnetic</a> forces become indistinguishable). <br />
<br />
The BICEP2 results also serve to constrain the theories of what happened during inflation. Several of these have been ruled out (e.g. large field <a href="http://en.wikipedia.org/wiki/Inflaton">inflation</a> models are now highly unlikely).<br />
<br />
Ultimately, these results need to be reproduced and refined by coming experiments. This doesn't mean that the scientific community isn't confident in BICEP2's results, but science needs to be reproducible. And in reproducing results, they are often refined and expanded upon. <br />
<br />
<div style="text-align: center;">
<b><span style="color: red;">This truly is an exciting time to be a scientist! </span></b></div>
<br />
<br />
<b>See Also: </b><br />
<br />
<ul>
<li>Archive of the BICEP2 press conference can be found <a href="http://www.cfa.harvard.edu/pao/Bicep2_news_con.mp4">here</a> (it is large so give it a little while to load).</li>
<li><a href="http://bicepkeck.org/">BICEP2 results page </a></li>
<li><a href="http://www.nytimes.com/2014/03/18/science/space/detection-of-waves-in-space-buttresses-landmark-theory-of-big-bang.html?_r=0">New York Time's article on BICEP2's results</a> with an excellent description of how inflation explains why the CMB has nearly the same temperature everywhere.</li>
<li><a href="http://www.newscientist.com/article/dn25235-first-glimpse-of-big-bang-ripples-from-universes-birth.html?full=true#.Uyyzjjzt4T4">New Scientist's article</a> on BICEP2 results</li>
</ul>
stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comLouisiana State University, Baton Rouge, LA 70803, USA30.4132579 -91.18000230000001230.3858694 -91.220342800000012 30.440646400000002 -91.139661800000013tag:blogger.com,1999:blog-4167914549123471212.post-72503639770135951222013-12-19T00:35:00.000-05:002013-12-19T00:44:07.662-05:00Silver and Gold: Clues to the History of Our Solar SystemIt's that time of year when many of us are buying gifts for our loved ones. And there's a song from the old <a href="http://en.wikipedia.org/wiki/Rudolph_the_Red-Nosed_Reindeer_%28TV_special%29">Rudolph the Red-Nosed Reindeer</a> TV special that comes to mind (sung by the character Yukon Cornelius): "Silver and gold, silver and gold. How many wonders can one cavern hold?..." But have you ever stopped to think about where your jewelery came from? I don't mean how your silver and gold was mined, but how was it created? It's much more interesting than anything you've probably imagined!<br />
<br />
<b>SILVER & GOLD</b><br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/-m22T7gy20X8/UrJ9Khb1DfI/AAAAAAAAA4I/tvqkM2kU1rw/s1600/Gold-crystals.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="207" src="http://4.bp.blogspot.com/-m22T7gy20X8/UrJ9Khb1DfI/AAAAAAAAA4I/tvqkM2kU1rw/s320/Gold-crystals.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Gold crystal (image from <a href="http://en.wikipedia.org/wiki/File:Gold-crystals.jpg">Wikipedia</a>)</td></tr>
</tbody></table>
<br />
First, let's go back to the birth of the Universe: <i><b>BANG!</b></i> (That was the Big Bang.) Sometime between 10 seconds and 20 minutes from now, the first atoms will be formed (this is called <a href="http://en.wikipedia.org/wiki/Primordial_nucleosynthesis">Big Bang nucleosynthesis</a>). These first atoms were of the simplest elements in the periodic table; mostly hydrogen and some helium and lithium. Even today, the most common elements in the Universe are hydrogen and helium. A few hundred million years later, clouds of this material will collapse to form the first stars. This birth is marked by the ignition of <a href="http://en.wikipedia.org/wiki/Nuclear_fusion">nuclear fusion</a>: the smashing of lighter elements together to make heavier ones. All stars start by smashing 2 hydrogen (H) atoms together to make a helium (He) atom. Eventually, the star will start to run out of hydrogen and will start to fuse helium to make beryllium (Be) and carbon (C). The largest stars will continue fusing atoms together until the product element is iron (Fe). For elements lighter than iron, smashing two lighter elements together to make a heavier element will release some energy. For elements heavier than iron, breaking an atom into two lighter atoms will release energy: this is called <a href="http://en.wikipedia.org/wiki/Nuclear_fission">nuclear fission</a>. So, the heaviest element that any star can normally make during its life is iron. Heavier elements like silver (Ag), gold (Au), and platinum (Pt) and many other elements can only be created in the most extreme environments such as a <a href="http://en.wikipedia.org/wiki/Supernova">supernova</a> explosion that marks the death of a star. <b>Therefore, the metal in our jewelery is truly a relic of a star that died before our Sun was born. </b><br />
<br />
Our Sun and solar system was born from the supernova explosion of an older star that died and, in doing so, seeded the material that makes up our solar system with heavier elements (this is the <a href="http://en.wikipedia.org/wiki/Nebular_hypothesis">nebular hypothesis</a>). For example, since the Earth is not a star it cannot perform nuclear fusion. Yet the core of our planet is primarily iron and nickel and had to be made in a previous star. This is what <a href="http://en.wikipedia.org/wiki/Carl_sagan">Carl Sagan</a> meant in his famous quote, "We are all starstuff."<br />
<br />
<br />
<b>WHAT ABOUT DIAMONDS?</b><br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-kwQA0SYzIU8/UrJ-JQxQBVI/AAAAAAAAA4U/6otQP4BaWac/s1600/Diamond.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://3.bp.blogspot.com/-kwQA0SYzIU8/UrJ-JQxQBVI/AAAAAAAAA4U/6otQP4BaWac/s1600/Diamond.jpg" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Diamond set into a gold ring (image from <a href="http://en.wikipedia.org/wiki/File:Diamond.jpg">Wikipedia</a>)</td></tr>
</tbody></table>
<br />
While I'm on the topic of the exotic origins of jewelery (and many other things), let me talk a little about why our Sun may turn into a giant diamond.<br />
<br />
First off, a diamond is made from carbon which our Sun is capable of making much later in its life (more on this in a little bit). Carbon is everywhere around us - pretty much every molecule that isn't water in your body has at least one carbon atom in it (this is the definition of an <a href="http://en.wikipedia.org/wiki/Organic_compounds">organic compound</a>). What makes a diamond special from all of the other common forms of carbon is that it has a very specific crystal structure that is only formed under extreme pressure and heat. (Any mineral that has the same chemical structure but a different crystalline organization is called a <a href="http://en.wikipedia.org/wiki/Polymorphism_%28materials_science%29">polymorph</a>.) So, the diamonds that are formed naturally on Earth started as a carbon deposit that transformed into a diamond under the extreme pressure and temperatures found beneath the surface of the Earth.<br />
<br />
What does this have to do with our Sun? Well, right now the Sun is busy turning hydrogen into helium. It will eventually (in about 5 billion years) start making heavier elements, but only <i>much more massive</i> stars ever have enough oomph (enough mass to create the most extreme pressures) to fuse elements all the way up to iron. Our Sun is not one of those stars (which is good since those massive stars live comparatively short lives). The Sun will only be able to produce up to carbon and oxygen (O) before fusion stops and the outer layers of the Sun are blown into the interstellar medium to seed future stars and solar systems. What is left behind is called a <a href="http://en.wikipedia.org/wiki/White_dwarf">white dwarf</a> composed of carbon that has been exposed to intense pressure and temperatures. <b>That means that the white dwarf our Sun leaves behind may very well be a diamond!</b><br />
<br />
A white dwarf that could be a massive diamond has already been observed and nicknamed <a href="http://en.wikipedia.org/wiki/BPM_37093">"Lucy"</a> (after the Beatles song "Lucy in the Sky With Diamonds"). It is more massive than the white dwarf our Sun will leave behind, but seems to be created by the same processes we expect for our Sun. All of this is very promising for a diamond to be the memorial for our Sun (and solar system).<br />
<br />
<br />
<b>WHAT DOES THIS HAVE TO DO WITH GRAVITATIONAL WAVES?</b><br />
<br />
Directly, not much. However, this past August it was confirmed that a <a href="http://en.wikipedia.org/wiki/Gamma-ray_burst#Short_gamma-ray_bursts">short gamma-ray burst</a> was the result of a <a href="http://en.wikipedia.org/wiki/Kilonova">kilonova</a>, the collision of two <a href="http://en.wikipedia.org/wiki/Neutron_star">neutron stars</a> that releases a massive amount of energy (read more about this <a href="http://o.canada.com/technology/hubble-confirms-kilonova-outburst/">here</a> and see my comments towards the end of the article). Neutron stars are the remnants of dead stars that were much more massive than our Sun (about 10 to 40 times the mass of our Sun) that died in a supernova. Those past supernovae would have created silver, gold, and everything heavier than iron and seeded the interstellar medium for future stars and solar systems. <br />
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These kilonova sources should produce copious amounts of gravitational waves, however, there has never been a short gamma-ray burst (like the one I mentioned above) detected close enough for LIGO to see it. Once Advanced LIGO is complete (soon!) the closest short gamma-ray burst will be just on the edge of the distance we expect to be able to detect these kinds of gravitational waves. But the great thing about what we do is that we really don't know how strong the gravitational waves from the actual explosion will be so they could very well be detectable in the future.<br />
<br />
Fingers crossed!stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.com19100 Ligo Road, Walker, LA 70785, USA30.562997199999991 -90.7742061999999815.0409626999999908 -132.08280019999998 56.085031699999988 -49.465612199999981tag:blogger.com,1999:blog-4167914549123471212.post-68396811401542947102013-10-08T17:15:00.003-04:002013-10-09T13:46:10.633-04:00Living LIGO's Belated 3rd AnniversaryThis past Saturday, 5 October, was the 3rd anniversary of the Living
LIGO blog (you can see the first ever post <a href="http://stuver.blogspot.com/2010/10/introduction.html">here</a>). I remember that because it also happens to be my birthday - I
started this out of a desire to do something I always wanted to so what
a better day to start than your own birthday. (If you must know, I've
just celebrated the 6th anniversary of turning 29.)<br />
<br />
I know it has been a long time since I've posted. I've been teaching at LSU and doing research at LIGO. On paper my life looks great but the reality is that there are many details, both personal and professional, that have added up to me not being in a great place for a while. I've been getting my jobs done but after that I've been pretty exhausted, at least mentally. This has happened to me before, so I thought I would direct you to my thoughts on what it's like being down but getting up again anyway <a href="http://stuver.blogspot.com/2011/06/slaying-my-own-dragons.html">here</a>. (Also see my last section below: "A WORD OF ADVICE...".)<br />
<br />
But there is one thought that has come up many times in the last few months: "I'd like to write a blog post on that." There are many different things, like continuing the series of posts I've started about methods of looking for gravitational waves or telling the story of where silver and gold come from (as in, how did it come to be on Earth). So, I am going to dig myself out of my slump and get back on my metaphorical horse - starting now!<br />
<br />
<br />
<b>WHAT I DID THIS SUMMER </b><br />
<br />
Let me tell you a little about what I've been doing since I've last posted. I got to go to a large meeting called the <a href="http://gr20-amaldi10.edu.pl/">GR20/Amaldi10 Meeting</a> in <a href="http://en.wikipedia.org/wiki/Warsaw">Warsaw</a>, Poland (where almost 850 gravity theorists and experimentalists gathered for this joint meeting) and gave 2 invited talks. The first was a formal talk on <a href="http://gr20-amaldi10.edu.pl/index.php?id=49&abstrakt=687">outreach skills and media</a> (featuring this blog) and the other was less formal and was on <a href="http://gr20-amaldi10.edu.pl/index.php?id=49&abstrakt=988">the benefits searching for gravitational waves can bring mankind focusing on spin-off technology</a> (I've written about this before <a href="http://stuver.blogspot.com/2012/06/q-how-can-gravitational-waves-help.html">here</a>).<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/-5IqTv-3DYW4/UlRr-5HQiWI/AAAAAAAAA0w/27-oBBvuxXk/s1600/2013-07-11+16.50.41.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="180" src="http://4.bp.blogspot.com/-5IqTv-3DYW4/UlRr-5HQiWI/AAAAAAAAA0w/27-oBBvuxXk/s320/2013-07-11+16.50.41.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">This is a picture of the gates of the <a href="http://en.wikipedia.org/wiki/Uniwersytet_Warszawski">Uniwersytet Warszawski</a> where GR20/Amaldi10 took place.</td></tr>
</tbody></table>
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/-dEa-GzkUkLI/UlRsBUNSvJI/AAAAAAAAA04/IkWLJOPGS0s/s1600/2013-07-11+16.50.30.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="180" src="http://4.bp.blogspot.com/-dEa-GzkUkLI/UlRsBUNSvJI/AAAAAAAAA04/IkWLJOPGS0s/s320/2013-07-11+16.50.30.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">A view through the gates at my colleagues on a coffee break in the distance.</td></tr>
</tbody></table>
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One of the best parts of meetings like this is that the meeting dinner is usually somewhere a normal person couldn't go. Our dinner was at the <i>in</i> the <a href="http://en.wikipedia.org/wiki/Royal_Castle,_Warsaw">Royal Castle in Warsaw</a>. And this is my husband and I on the lawn beforehand:<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-smP6Pk_A1-U/UlRtHqCNH7I/AAAAAAAAA1E/uQmFQlchUmA/s1600/2013-07-10+19.21.14.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="180" src="http://1.bp.blogspot.com/-smP6Pk_A1-U/UlRtHqCNH7I/AAAAAAAAA1E/uQmFQlchUmA/s320/2013-07-10+19.21.14.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">My husband, Derek, and I on the lawn behind the Royal Castle in Warsaw, Poland.</td></tr>
</tbody></table>
<br />
Just before my trip to Warsaw, I took a short holiday to <a href="http://en.wikipedia.org/wiki/Paris,_France">Paris</a>, France. There was a debacle with lost luggage and then wrong luggage being delivered to us, but outside of wearing the same clothes for a few days (this is why I always pack extra underwear in my carry-on luggage), my husband and I had a great time just relaxing and wondering around. My new phone takes panoramic pictures and this is a good one I got of the <a href="http://en.wikipedia.org/wiki/Louvre">Louvre</a>:<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-uXts4MBQiLA/UlRt09GFPqI/AAAAAAAAA1M/PDcKLAU6AiM/s1600/2013-07-06+19.18.22.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="38" src="http://3.bp.blogspot.com/-uXts4MBQiLA/UlRt09GFPqI/AAAAAAAAA1M/PDcKLAU6AiM/s400/2013-07-06+19.18.22.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Panoramic view of the <a href="http://en.wikipedia.org/wiki/Louvre">Louvre</a> (Paris, France)<br />
<b>Click on the picture for a larger view.</b></td></tr>
</tbody></table>
<br />
Once I returned home to the United States, I had tons of work to do. I've talked before about how LIGO has been testing its data infrastructure to prepare for Advanced LIGO <a href="http://stuver.blogspot.com/2012/01/first-software-engineering-run-for.html">here</a>. We are then had our 4th software engineering run; that means that I had to improve upon the gravitational wave simulation software I wrote to perform better, faster, and incorporate more features. It was a bit stressful come the deadline, but it all got done and turned out well.<br />
<br />
<br />
<b>... AND THEN SCHOOL STARTED AGAIN</b><br />
<br />
Then school started again. I am teaching (at LSU) the first semester of physical science (sometimes referred to as "Physics for Poets" since it is more conceptually based than mathematically focused). Most of my students in this class (this year my lecture has only about 100 students) are elementary education majors. Some might think that teaching an "easy" class like this would be, well... easy. But it is far from it. The less math you can rely on to teach the subject matter, the better you have to be as a teacher in communicating what the math means. Since I love challenges like this, this is one of my favorite classes to teach. I am also team teaching a junior/senior level class on Science Methods for secondary education pre-service teachers majoring in science or math. This class shows them how science is done by doing experiments using the scientific method, analyzing their data and reporting it in both papers and presentation (since these are the two main means that scientists communicate with each other).<br />
<br />
At LIGO, I am working on a paper with a group of other LIGO scientists who are looking for gravitational waves from supernovae that may have occurred while LIGO and/or other gravitational wave observatories were in operation (before the advanced detector upgrade began). And, as always, I continue to refine my gravitational wave simulation software.<br />
<br />
<br />
<b>A QUICK WORD OF ADVICE...</b><br />
<br />
I'll be writing again soon (probably next week). When I first started this blog, I promised you a peek into the life of a working scientist. Lately I've been answering lots of questions about gravity and how to look for gravitational waves. But since there has been something major going on in my life, and it kept me from writing my blog as I would have liked, I wanted to share that with you.<br />
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I am lucky since even though I know I have times when depression can get the better of me, I have wonderful support from my husband, friends, and family. I'm not sure why, but they all seem to love me even when I can't stand to be around myself. <br />
<br />
<b>For anyone reading this who has issues with depression and/or anxiety:</b> Don't fool yourself that everything you are feeling inside is not affecting you because you may be able to keep it together and have others think you are happy. This will eat at you and everything you are feeling will come out sometime (and usually at the least opportune time). If you are sad or anxious for long periods of time, even if it's on-and-off, find some help. It is not weak to seek help (I've been told that before and it's usually by people who need help for themselves and are too afraid to get it). It takes an inner strength to admit when you are hurting and need a hand up, an ear to listen to you, or a shoulder to cry on. If that's not enough, talk to your doctor. Not once has a doctor been anything but 100% supportive of me when I've gone to them seeking medical help. NOT ONCE did they look down on me, or suggest that my feelings will pass, or that I need to "buck up". With support and help, I've always clawed my way back to feeling like a normal person. You can too!stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.com19100 Ligo Road, Walker, LA 70785, USA30.562997199999991 -90.7742061999999815.0409626999999908 -132.08280019999998 56.085031699999988 -49.465612199999981tag:blogger.com,1999:blog-4167914549123471212.post-4522748182586732442013-06-30T22:32:00.001-04:002013-07-02T10:00:48.768-04:00Methods of Detecting Gravitational Waves I: Resonant-Mass DetectorsAs the name of this blog suggests, I use LIGO and similar gravitational-wave detectors (like Virgo and GEO). These detectors are all interferometric detectors meaning that they use the interference of light to measure gravitational waves. But interferometers were not the first means used to look for gravitational waves...<br />
<br />
<b>WEBER BARS</b><br />
<br />
In 1966, <a href="http://en.wikipedia.org/wiki/Joseph_Weber">Joseph Weber</a> of the University of Maryland constructed a gravitational-wave detector that consisted of a very precisely machined cylinder of aluminum 2 meters long and 1 meter in diameter. The idea was that when a gravitational wave passed over the bar at a specific frequency, the bar would start to ring like a bell. This "ringing" frequency, also called the <a href="http://en.wikipedia.org/wiki/Resonance">resonant</a> frequency, for Weber's bars was 1660 Hz (cycles per second).<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-X9S9dlHc3V0/UdGoEH7n_qI/AAAAAAAAAx0/zljSnpDZm4A/s493/Weber.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="270" src="http://2.bp.blogspot.com/-X9S9dlHc3V0/UdGoEH7n_qI/AAAAAAAAAx0/zljSnpDZm4A/s320/Weber.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Weber working on one of his bars at the University of Maryland, c. 1965.</td></tr>
</tbody></table>
<br />
The way these bars are be used to detect gravitational waves involves the phenomenon of <a href="http://en.wikipedia.org/wiki/Sympathetic_resonance">sympathetic resonance</a>. This is when the vibration of something external to an object matches its resonant or "ringing" frequency and causes it to begin vibrating. Even after the external vibration stops, the now vibrating object will continue to ring like a bell (and eventually stop ringing just like a bell as well).<br />
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Now, when a gravitational wave at or very near to 1660 Hz passes by one of Weber's bars, it will stretch space in one direction and compress it in the perpendicular direction, much like illustrated in the animation below:<br />
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<a href="http://1.bp.blogspot.com/-GTmfhzf7umY/T-R6z9iLeYI/AAAAAAAAAxQ/LhzDdAKkUjE/s288/GWeffect.gif" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://1.bp.blogspot.com/-GTmfhzf7umY/T-R6z9iLeYI/AAAAAAAAAxQ/LhzDdAKkUjE/s288/GWeffect.gif" /></a></div>
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This stretching and compressing is the vibration that makes the bar 'ring'.<br />
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<div style="text-align: left;">
One property of gravitational waves is that even the strongest of them that we can hope to detect on Earth are exceedingly weak. Because of that, any ringing of the bar will be too small to hear or even to detect using normal ways of measuring vibration. Instead, crystals that produce an electric voltage when stretched or compressed (called a <a href="https://en.wikipedia.org/wiki/Piezoelectricity">piezoelectric crystal</a>) were mounted around the bar. Measuring the voltage from these crystals is also measuring the motions of the bar that could be from it ringing. </div>
<br />
But just like there are many things other than gravitational waves that can cause <a href="http://en.wikipedia.org/wiki/Noise">noise</a> in the data that LIGO collects, there were many other things that could cause the motion of Weber's bars. Even the <a href="http://en.wikipedia.org/wiki/Thermal_motion">vibration of the aluminum atoms in the bar due to their temperature</a> (Weber's bars were kept in a vacuum at room temperature) created significant noise and limited how small of a gravitational wave they could detect. Ultimately, they were limited to a <a href="http://en.wikipedia.org/wiki/Deformation_%28mechanics%29">strain</a> (which is defined to be the change in length divided by the original length of an object) of about 10<sup>-16</sup>. To give this scale some reference, a "large" gravitational wave to LIGO would produce a strain of about 10<sup>-21</sup> and we think we can expect a gravitational wave this large about once every 10 years! But, it is still possible that Weber's bars could have detected gravitational waves...<br />
<br />
By 1969 Weber thought that he may have detected gravitational waves
with his bar detectors and continued to make several claims over the
years but none were regarded as significant enough to declare that the
first elusive gravitational wave had truly been directly observed. These claims were ultimately not accepted for many reasons including that other groups were
not able to reproduce his rate of detections which Weber was claiming to be up to several a day. Weber lost the financial support of the National Science Foundation (which now funds LIGO) after a disputed claim of the detection of gravitational waves from a supernova observed in February 1987 (<a href="https://en.wikipedia.org/wiki/SN_1987A">SN1987A</a>).<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-UM8iz25HPyI/UdHreRupCxI/AAAAAAAAAyE/cPaswUeco1M/s640/LIGO0025.JPG" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="240" src="http://3.bp.blogspot.com/-UM8iz25HPyI/UdHreRupCxI/AAAAAAAAAyE/cPaswUeco1M/s320/LIGO0025.JPG" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">One of Weber's original bars on display at the LIGO Hanford Observatory in August 2004.</td></tr>
</tbody></table>
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There are <i><b>many</b></i> more interesting details surrounding Weber's career that I will write a post on later. But while the controversy surrounding his claims of detection do not seem to cast him in a favorable light, it was through his work that others became inspired to look for gravitational waves in different ways, including using an interferometer like LIGO does. Joseph Weber is truly the father of the search for gravitational waves!<br />
<br />
<br />
<b>MODERN BARS</b><br />
<br />
Since Weber, there have been many advancements in using resonant-mass bars to detect gravitational waves. Most bars today are made from new aluminum alloys, are cryogenically cooled to reduce the noise from the bar's thermal vibrations, have mechanical means to amplify the vibration, and piezoelectric crystals have been replaced with even more sensitive motion sensors. Different shapes (like spheres) have also been used to increase sensitivity to gravitational waves coming from different directions because bars are most sensitive to gravitational wave directly above or below the bar.<br />
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<br />
<b>COMPARISON TO DETECTORS LIKE LIGO</b><br />
<br />
Resonant-mass gravitational-wave detectors like Weber's bars and interferometric detectors like LIGO look for the same effect: the stretching and compressing of space caused by the gravitational wave. Bars are far less expensive than detectors like LIGO but are only sensitive to narrow ranges of gravitational wave frequencies. Bars are also only sensitive to small portions of the sky at once where detectors like LIGO are sensitive to most of the sky at once (including the sky on the other side of the planet). But because of how each of these detectors look for gravitational waves, resonant-mass detectors are likely to only be sensitive to the strongest gravitational waves.<br />
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<br />
<b>THE DETECTORS RIGHT NOW</b><br />
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If you are interested in the operational state of gravitational-wave detectors (including resonant-mass detectors) click <a href="http://www.ldas-sw.ligo.caltech.edu/ligotools/runtools/gwistat/" target="_blank">here</a>. <a href="https://en.wikipedia.org/wiki/AURIGA" target="_blank">AURIGA</a> and <a href="http://www.lnf.infn.it/esperimenti/rog/frame_nautilus.htm" target="_blank">NAUTILUS</a> are both bar detectors while <a href="http://www.lnf.infn.it/esperimenti/rog/frame_nautilus.htm" target="">GEO 600</a>, <a href="http://www.ligo.org/" target="">LIGO</a>, and <a href="https://en.wikipedia.org/wiki/Virgo_interferometer" target="">Virgo</a> are interferometers.stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comBaton Rouge, LA 70810, USA30.350581299999991 -91.08735509999996830.240967799999993 -91.248716599999966 30.460194799999989 -90.92599359999997tag:blogger.com,1999:blog-4167914549123471212.post-84024025006128166202013-05-21T17:20:00.000-04:002013-05-22T14:52:41.618-04:00Here's Your Chance to Help LISA Happen!<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-uIIcakd74qM/UZvkLilcP_I/AAAAAAAAAv4/qs1UcPKal_E/s1600/lisalaser.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="77" src="http://3.bp.blogspot.com/-uIIcakd74qM/UZvkLilcP_I/AAAAAAAAAv4/qs1UcPKal_E/s400/lisalaser.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">A depiction of a LISA satellite with its lasers. </td></tr>
</tbody></table>
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I've written about LISA several times on this blog and most of those times the news hasn't been good. Today I have a bit of encouraging news and a way for you to help!<br />
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For readers who've recently found Living LIGO, LISA is a space-based gravitational wave detector that will be sensitive to lower frequency gravitational waves than any Earth-based counterpart ever will be. Gathering gravitational-wave information from low frequencies will help complete the picture that gravitational-wave astronomy can paint; Earth-based detectors are really only sensitive to the "death throes" of violent astrophysical interactions while LISA will be sensitive to these same sources in their youth. This youth stage is so long that the predominant noise source for LISA is continually measuring the gravitational waves from these young sources coming from all over the sky at the same time. This is called the "confusion limit" and it is like trying to listen to a conversation on the other side of the room at a busy party. This can be overcome, but what a wonderful problem to have! The noise you measure is really just measuring so many gravitational waves at the same time that they mix together!<br />
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You can follow the unfolding of the LISA drama through these Living LIGO posts:<br />
<br />
<ul>
<li><a href="http://stuver.blogspot.com/2012/05/news-on-lisa-and-some-personal-stuff.html">News on LISA</a> [25 May 2012] </li>
<li><a href="http://stuver.blogspot.com/2012/05/more-on-lisango-and-what-would-you-ask.html">More on LISA/NGO</a> [3 May 2012]</li>
<li><a href="http://stuver.blogspot.com/2012/04/likely-end-to-space-based-gw-detector.html">The Likely End to a Space-Based GW Detector</a> [19 April 2012] (The title turned out to be over dramatic - I'm glad!) </li>
</ul>
<br />
In the "News on LISA" (25 May 2012) post, the statement from the eLISA Consortium was that they were going to push for the next launch opportunity. The European Space Agency has initiated the process to choose candidate missions for the next launch. <span style="color: red;"><b>The eLISA mission team is looking for your support! </b></span><br />
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<b>HOW YOU CAN HELP...</b><br />
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Please go to the <a href="http://support.elisascience.org/">eLISA - Make History</a> page and sign your name as a supporter. Anyone from around the would can lend their support. If you are a scientist, you can also opt to have your name and institution listed in the eLISA white paper. (You can see the <a href="http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=51454">ESA's call for white papers</a> here.)<br />
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If you support gravitational-wave science at any level, please consider putting your name on the list! Let's show the world that there is true support for this science!<br />
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<span style="color: red;"><b>HURRY! There are only 2 days (or less) to add your name to the list of supporters! </b></span><br />
<span style="color: red;"><b><a href="http://support.elisascience.org/">eLISA - Make History</a> </b></span></div>
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<b>NEW LISA YOUTUBE CHANNEL</b><br />
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The LISA Mission has also created <a href="http://www.youtube.com/user/LISAcommunity?feature=watch">their own YouTube channel</a> and is starting to post some truly exceptional animated educational videos. Right now, two are available:<br />
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<b>Gravity Ink. - Einstein's Gravity (Episode 1)</b></div>
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<b>Gravity Ink. - The Future of Astronomy (Episode 2)</b></div>
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Consider subscribing to their <a href="http://www.youtube.com/user/LISAcommunity?feature=watch">YouTube channel</a> to keep up on new installments (I will most likely feature them here too!). </div>
<br />stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.com19100 Ligo Road, Walker, LA 70785, USA30.562997199999991 -90.7742061999999813.2719371999999893 -132.08280019999998 57.854057199999993 -49.465612199999981tag:blogger.com,1999:blog-4167914549123471212.post-29536570437226265932013-03-29T16:49:00.000-04:002013-03-29T19:04:06.303-04:00Black Holes 101Most of what I discuss on this blog has to do directly with <a href="http://stuver.blogspot.com/2012/05/q-what-is-gravitational-wave.html">gravitational waves</a>. This time I'd like to talk about one of their most talked about exotic sources: <a href="http://en.wikipedia.org/wiki/Black_hole">black holes</a>. Black holes are an exemplary source because they are highly concentrated mass. Just add a touch of accelerated motion and gravitational waves are emitted in abundance (well, it's not quite that simple and "abundance" is a relative term, but you get the idea). But what are the fundamental concepts that add up to the existence of black holes? That's what we are focusing on now.<br />
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<b>1. Escape velocity</b><br />
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You've probably noticed that the harder you throw an ball straight up in the air, the higher it goes. We also know that the farther away the ball gets from the Earth, the lower the gravitational attraction is between the ball and the Earth. When you connect these two concepts, you can imagine that there is a speed at which you can throw the ball up and it will never come back down. This is called the <a href="http://en.wikipedia.org/wiki/Escape_velocity">escape velocity</a>:<br />
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<a href="http://4.bp.blogspot.com/-sfo2EYsvi_U/UJKzX8Jmm6I/AAAAAAAAAes/1oKyAo7YdnY/s1600/escv.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://4.bp.blogspot.com/-sfo2EYsvi_U/UJKzX8Jmm6I/AAAAAAAAAes/1oKyAo7YdnY/s1600/escv.png" /></a></div>
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We have discussed escape velocity before on this blog (specifically when discussing <a href="http://stuver.blogspot.com/2012/11/gravity-love-story-ii-starstruck.html">the conditions an object must have to be 'eaten' by a black hole</a>). In this equation, <b>G</b> is the <a href="http://en.wikipedia.org/wiki/Gravitational_constant">gravitational constant</a>, <b>M</b> is the mass of the 'thing' you are trying to escape, and <b>r</b> is the distance you are from the center of the 'thing'. The bigger the mass of the 'thing', <b>M</b>, is, the faster the object must be thrown to escape it, <b>v<sub>e</sub></b>.<br />
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Going back to throwing a ball up in the air from the Earth's surface, you would need to throw that ball about 25,000 mph so that the ball would not come back to the Earth (good luck with that)!<br />
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<b>2. The speed of light is the universal 'speed limit'</b><br />
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Nothing can travel faster than the <a href="http://en.wikipedia.org/wiki/Speed_of_light">speed of light</a>
(in a vacuum), represented by <b>c</b>. No matter, energy, or information about the Universe
can travel faster than that. That is pretty much the long and the short
of this concept.<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-god78OhcRCQ/UVXl4gJT8yI/AAAAAAAAAuc/y6EE_rd3jRY/s1600/Speed_Limit_C.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://2.bp.blogspot.com/-god78OhcRCQ/UVXl4gJT8yI/AAAAAAAAAuc/y6EE_rd3jRY/s1600/Speed_Limit_C.png" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">[Source: <a href="http://ksj.mit.edu/tracker/2012/03/fast-ink-and-whoa-there-they-clocked-mor">Knight Science Journalism at MIT blog</a>]</td></tr>
</tbody></table>
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This 'speed limit' comes from Einstein's special relativity and the effect of <a href="http://en.wikipedia.org/wiki/Relativity_of_simultaneity">simultaneity</a>.
Perhaps I will write a longer post about this in the future, but all
that is important now is to recognize that if something needed to travel
faster than the speed of light to communicate information to you, then
you are never going to know about it.<br />
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<b>3. Light is affected by gravity</b><br />
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Light is both a particle and a wave. As a particle, it has no mass. Since gravity acts between two masses, it may be surprising that light can be affected by gravity at all! But it does. This effect is called <a href="http://en.wikipedia.org/wiki/Gravitational_lens">gravitational lensing</a> and I've written about this previously <a href="http://stuver.blogspot.com/2012/07/the-journey-of-gravitational-wave-ii-gw.html">here</a>. <br />
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<b>CONCLUSION: How these concepts form a black hole</b><br />
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The simplest black hole is called a <a href="http://en.wikipedia.org/wiki/Schwarzschild_black_hole">Schwarzschild black hole</a>. This is a black hole that has no electrical charge and is not rotating - it's just "there" meaning that there won't be anything to complicate our black hole situation. For now, let us think of our black hole as having mass but no volume. You can think of this as being the ultimate implosion. Since this mass has no volume, there isn't any surface to it. Eventually, as we get closer and closer to where the mass is centered, the escape velocity will become so large that the escape velocity will be greater than the speed of light. And since light is indeed affected by gravity, that means that nothing will be able to escape the black hole. We can even figure out what this distance is from the equation for escape velocity by setting <b>v<sub>e</sub></b> to the speed of light, <b>c</b>, and solving for <b>r</b> (the distance away from the mass where the escape velocity equals the speed of light):<br />
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<a href="http://2.bp.blogspot.com/-EQEiDnAWNYY/UVX3OWGa49I/AAAAAAAAAus/iM3cMqtmb-E/s1600/eventhorizonEQ.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://2.bp.blogspot.com/-EQEiDnAWNYY/UVX3OWGa49I/AAAAAAAAAus/iM3cMqtmb-E/s1600/eventhorizonEQ.png" /></a></div>
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This distance from a black hole where light will not be able to emerge from a black hole is also called the <a href="http://en.wikipedia.org/wiki/Event_horizon">event horizon</a> and this sphere around the black hole is what is being referred to when we talk about the size of the back hole. For this simple Schwarzschild black hole, it is also known as the <a href="http://en.wikipedia.org/wiki/Schwarzschild_radius">Schwarzschild radius</a>. You can also think of this radius as how small a mass would have to be to become a black hole. </div>
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So, how big would the Schwarzschild radius be for some things we are familiar with? Well, for a black hole with the mass of our Sun it would be just about 3 km or about 1.9 miles. For a black hole with the mass of the Earth it would be 8.87 mm or a little under 11/32" (0.349 in).</div>
stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.com19100 Ligo Road, Walker, LA 70785, USA30.562997199999991 -90.7742061999999813.2719371999999893 -132.08280019999998 57.854057199999993 -49.465612199999981tag:blogger.com,1999:blog-4167914549123471212.post-36975577230502864222013-02-28T23:38:00.001-05:002013-10-08T23:07:34.828-04:00Lessons From My Childhood on How to TeachOne of the best parts of my job is getting to do outreach. This is going out and teaching the public about the research that I do. Since I love what I do and those that I encounter are usually interested in what I have to say or they wouldn't be there (like you wouldn't be reading this if you didn't want to), it is almost always a rewarding experience all around. However, I had some childhood experiences with outreach that were, well, a little traumatic. However, they have taught me lessons that I use every time I teach whether in the classroom, engaging the public at LIGO, or writing for you.<br />
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<b>"HAIR-RAISING" TRAUMA</b><br />
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Ever since I was a young child, I've always known that where I am now is where I wanted to be. That is, I've always known that I wanted to be a <a href="http://en.wikipedia.org/wiki/Physicist">physicist</a> or an <a href="http://en.wikipedia.org/wiki/Astronomer">astronomer</a>. Of course, that's not what I said; I wanted to be an <a href="http://en.wikipedia.org/wiki/Astronaut">astronaut</a> since that is the hero job for the <a href="http://en.wikipedia.org/wiki/Physical_science">physical sciences</a>. My family has also been supportive of me and one of my favorite things to do was go to the <a href="http://en.wikipedia.org/wiki/Planetarium">planetarium</a>. At the time, I lived outside of <a href="http://en.wikipedia.org/wiki/Pittsburgh,_Pennsylvania">Pittsburgh, PA</a> and we would go to the <a href="http://en.wikipedia.org/wiki/Buhl_Planetarium">Buhl Planetarium</a> (before it became part of the newer <a href="http://www.carnegiesciencecenter.org/">Carnegie Science Center</a> - the building is now part of the <a href="https://pittsburghkids.org/">Children's Museum of Pittsburgh</a>).<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-9UkVgQH9cwE/UTAjK2hm_fI/AAAAAAAAAs4/rULD3KNu7-c/s1600/BuhlPlanetarium.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="320" src="http://1.bp.blogspot.com/-9UkVgQH9cwE/UTAjK2hm_fI/AAAAAAAAAs4/rULD3KNu7-c/s320/BuhlPlanetarium.jpg" width="299" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Front entrance of the Buhl Planetarium in Pittsburgh, PA. [Source: <a href="http://en.wikipedia.org/wiki/File:BuhlPlanetariumInstitutePopularScience.jpg">Wikipedia</a>]</td></tr>
</tbody></table>
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On the fateful trip in question, I was no more than 7 or 8 years old and I was watching a demonstration in between planetarium shows with my father. The presenter asked for a volunteer from the crowd, preferably with long fine hair. The next thing I felt is my father's hand on my back pushing me forward. I wasn't interested in being the center of attention, but the presenter thought that I would be perfect for the role.<br />
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She called me forward and had me stand on a plastic milk crate beside a metal dome that was bigger than my head. She told me that I was going to have to hold on the the metal dome with one hand but I was not to do a list of things or I would get hurt. Then I was <i>worried</i>. She had me put one hand on the dome and turned the machine on. It made a lot noise and I feel an odd tingling over my skin. Then I was <i>scared</i>. The presenter was very happy about everything and told me to shake my head. I did so timidly. Then she encouraged me to shake my head with more vigor. I shook the heck out of my head so she would leave me alone and I could be done with all of this. Then EVERYONE who is watching this demonstration WAS LAUGHING AT ME. Then they applauded as the machine was turned off and I was helped down from my perch and left to think I was being laughed at.<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-Z3dO3_JJrh0/UTAltp3wGbI/AAAAAAAAAtI/DrJQApuM9q4/s1600/vdgGenerator.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="320" src="http://1.bp.blogspot.com/-Z3dO3_JJrh0/UTAltp3wGbI/AAAAAAAAAtI/DrJQApuM9q4/s320/vdgGenerator.jpg" width="203" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The machine with the big metal dome attached to the top. I later discovered that this is a <a href="http://en.wikipedia.org/wiki/Van_de_Graaff_generator">Van de Graaff generator</a>. [Source: <a href="http://courseware.phys.unm.edu/vem/lab2.html">UMN Physics department</a>]</td></tr>
</tbody></table>
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It wasn't until I was in middle school that I figured out why everyone was laughing at me. That machine was a <a href="http://en.wikipedia.org/wiki/Van_de_Graaff_generator">Van de Graaff generator</a> and it deposited <a href="http://en.wikipedia.org/wiki/Static_electricity">static electricity</a> on me. The warnings that worried me were to prevent me from getting "zapped" and everyone was laughing at me because my hair was standing on end. The harder I shook my head, the more the static electricity made my hair stand out. A lot like this:<br />
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<iframe allowfullscreen='allowfullscreen' webkitallowfullscreen='webkitallowfullscreen' mozallowfullscreen='mozallowfullscreen' width='320' height='266' src='https://www.youtube.com/embed/bO91e0AaGGg?feature=player_embedded' frameborder='0'></iframe></div>
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<b><span style="color: magenta;"><u>WHAT WENT WRONG?</u>:</span> </b> The presenter didn't show me what I looked like in a mirror (as is featured in the clip above) or tell me what I looked like. I had no idea why everyone was laughing at me or what the point of the "hair raising" demonstration was. Without this knowledge, I walked away from the experience thinking that everyone was really laughing at ME and not the effects of static electricity.<br />
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<span style="color: magenta;"><b><u>LESSON LEARNED</u>:</b></span> If you use a volunteer in a demonstration, make sure that they understand what is happening.<br />
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I don't have many occasions where I need a volunteer for a demonstration, but when I do I make the volunteer the focus of the demonstration so that, at the very least, they walk away understanding what happened. <br />
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Read more about <a href="http://science.howstuffworks.com/transport/engines-equipment/vdg.htm">how Van de Graaff generators work</a>.<br />
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<b>SWINGING FOR A "BREAKTHROUGH"</b><br />
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When I was too young for school, I wanted to be a big girl and play school. Even then I loved science. One day I convinced my father to play school with me. Using the sliding green chalk board doors on my toy box, my father taught me about the <a href="http://en.wikipedia.org/wiki/Structure_of_the_Earth">layers of the Earth</a>.<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-kh12giBqbI0/UTAnaF7hSCI/AAAAAAAAAtY/2NX1i0uQSLI/s1600/toy-box.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="213" src="http://1.bp.blogspot.com/-kh12giBqbI0/UTAnaF7hSCI/AAAAAAAAAtY/2NX1i0uQSLI/s320/toy-box.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">A toy box much like the one my father used to play school with me. [Source: <a href="http://itsstilllife.com/2011/08/03/would-you-buy-it-wednesday-3/">It's Still Life</a> blog]</td></tr>
</tbody></table>
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The Earth's layers can be generalized into 4 main layers: the <a href="http://en.wikipedia.org/wiki/Crust_%28geology%29">crust</a> at the surface where we live, then the <a href="http://en.wikipedia.org/wiki/Mantle_%28geology%29">mantle</a>, and finally the <a href="http://en.wikipedia.org/wiki/Outer_core">outer</a> and <a href="http://en.wikipedia.org/wiki/Inner_core">inner cores</a>.<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/-aU5E7cuVADo/UTArieKy5TI/AAAAAAAAAt0/YTX4ssa26f0/s1600/layersEarth.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="242" src="http://4.bp.blogspot.com/-aU5E7cuVADo/UTArieKy5TI/AAAAAAAAAt0/YTX4ssa26f0/s320/layersEarth.png" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Diagram showing the layers of the Earth. [Source: <a href="http://everythingabouttheearth.blogspot.com/2011/09/earths-layer.html">About Earth</a> blog]</td></tr>
</tbody></table>
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I was told that the crust was <b>very thin</b> and the mantle is hot molten rock (<a href="http://en.wikipedia.org/wiki/Magma">magma</a>) [note: only the mantle near the outer core is molten but the mantle under the crust is about 1000<sup>o</sup>F so I equated that to "molten" too as a child]. I'd seen documentaries about <a href="http://en.wikipedia.org/wiki/Volcano">volcanoes</a> on television and knew what "molten rock" meant. This completely changed the way I saw the swing set in my back yard. Why? Well, have you noticed the divot under the swings where you drag your feet to slow the swing to a stop? I saw that as eating away at the crust and I was afraid that I would break through to the mantle and sink my feet into molten rock! I know that it really isn't logical since I'd seen deeper holes before and there was nothing but dirt at the bottom, but I was a little kid and didn't think like that. Anyway, I then was afraid of breaking through the crust if I dragged my feet and I was too chicken to jump off. That left me sitting on the swing waiting for it to slow down on its own. The wait took a lot of the fun out of swinging! <br />
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<span style="color: magenta;"><b><u>WHAT WENT WRONG?</u>:</b></span> The scale of "thick" and "thin" was not established. When I heard that the crust was thin, I defined for myself what "thin" was. I assumed it was only as deep as I could dig through it. What "thin" really meant is compared to the size (radius) of the Earth.<br />
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For the record, the radius of the Earth is almost 4,000 miles and the crust is up to about 22 miles. Since 22 miles is much, much less than 4,000 miles, the crust is indeed "thin" <u>compared to the size of the Earth</u>! <br />
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<span style="color: magenta;"><b><u>LESSON LEARNED</u>:</b></span> When you tell someone that something is "big" or "small", make sure you establish what you are comparing that something to, i.e. make sure you set the scale for your comparison.<br />
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I sometimes tell this story after I admonish people to always ask a scientist how big or small they think "big" or "small" are. I tell them that I think a "big" <a href="http://stuver.blogspot.com/2012/05/q-what-is-gravitational-wave.html">gravitational wave</a>, one that we would only expect to see every 10 years or so, would change the length of <a href="http://www.ligo.org/">LIGO</a>'s 4 km (2.5 mile) long arms less than 1/1000<sup>th</sup> the diameter of a <a href="http://en.wikipedia.org/wiki/Proton">proton</a> (10<sup>-18</sup> m). That may be "big" to me now, but to a 5-year-old me something smaller than an <a href="http://en.wikipedia.org/wiki/Atom">atom</a> would be most certainly be considered "small". stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comBaton Rouge, LA 70810, USA30.350581299999991 -91.08735509999996830.240967299999991 -91.248716599999966 30.460195299999992 -90.92599359999997tag:blogger.com,1999:blog-4167914549123471212.post-60323876525103429612013-01-18T18:23:00.000-05:002013-01-18T21:27:07.752-05:00Q: What's the Difference Between a "Gravitational Wave" and a "Gravity Wave"?The things that LIGO looks for are called <b>gravitational waves</b> (which are discussed in depth <a href="http://stuver.blogspot.com/2012/05/q-what-is-gravitational-wave.html">here on my blog</a> and on the <a href="http://www.ligo.org/science.php">LIGO website</a>). That can be a mouthful, especially when having a conversation about them. People, including us professionals, realize this and often take the shortcut of calling them "<b>gravity waves</b>". It sounds so similar that this must mean the same thing, right? Well, <u><b>no!</b></u><br />
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<b>GRAVITY WAVES ARE <u>NOT</u> GRAVITATIONAL WAVES</b><br />
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The proper technical use of <a href="http://en.wikipedia.org/wiki/Gravity_wave">gravity wave</a> refers to waves on the interface of two fluids, which can be liquid and/or gas. Where this boundary is disturbed, gravity will pull it down and buoyancy will push it up. This combination of opposite push and pull creates a wave that moves out over the surface. You can make your own interface of two fluids by filling a glass with some water and oil:<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/-xR-Euy9PL0Y/UPnACWaZo7I/AAAAAAAAAsg/Pz3fP5pgg30/s1600/Water_and_oil.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="320" src="http://4.bp.blogspot.com/-xR-Euy9PL0Y/UPnACWaZo7I/AAAAAAAAAsg/Pz3fP5pgg30/s320/Water_and_oil.jpg" width="240" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">A glass containing oil and water. Oil settles at the top because it is less dense (more buoyant). [Source: <a href="http://en.wikipedia.org/wiki/File:Water_and_oil.jpg">Wikipedia</a>]</td></tr>
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Water and oil will separate if left alone. This separation creates a boundary between the oil and water with the oil on top since it is less dense. Now imagine gently tapping on the side of the glass. The vibration
from your tap will transfer into the separated oil and water which will produce a gravity wave on their boundary. If you actually do this carefully enough, you can produce a gravity wave ONLY on the oil/water boundary and not on the surface of the oil (though a surface wave on the oil is technically a gravity wave too since that is a liquid/gas fluid boundary).<br />
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While the oil and water example technically illustrates a gravity wave, the term is usually applied to gravity waves that occur in nature. Examples include:<br />
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<ul>
<li>The waves on water caused by wind from large ocean waves to ripples in a puddle; these are examples of gravity waves on an gas/liquid boundary. </li>
<li>Waves of different density waters under the oceans' surface (like warm/cool water, or fresh/salt water); these are examples of a liquid/liquid boundary.</li>
<li>The rippling of clouds, like in the movie below; this is an example of a gravity wave on a gas/gas boundary.</li>
</ul>
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<div class="separator" style="clear: both; text-align: center;">
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<br />
<br />
<br />
<b>CAN A GRAVITATIONAL WAVE DETECTOR DETECT GRAVITY WAVES TOO?</b><br />
<br />
We've now established that a <i>gravity wave</i> is very different from the <i>gravitational waves</i> that LIGO is looking for. But can LIGO detect them anyway? Indirectly, yes! Almost three-quarters of the Earth is covered by oceans. These oceans are roiling with gravity waves both within the water and on top of it. When these waves encounter solid earth, much of the wave is reflected but some of the energy is absorbed. This absorbed energy can then create surface waves on the remaining part of the Earth's surface that is solid. These ground vibrations are called <a href="http://en.wikipedia.org/wiki/Microseism">microseism</a>.<br />
<br />
Since LIGO lives on the Earth's surface (many people think that LIGO is underground but it really is built above ground), these vibrations shake the detector and contribute to the measured detector noise. So much so that, compared to the gravitational waves we seek, we don't expect to be able to detect low <a href="http://en.wikipedia.org/wiki/Frequency">frequency</a> (less than about 10 Hz or so) gravitational waves. And it doesn't matter that both LIGO detectors are near shores since the microseism shakes the entire Earth - we could have built LIGO in the middle of Nebraska and the microseism would still negatively affect us. <br />
<br />
In order to detect low frequency gravitational waves, we need to get away from the microseism. The proposed gravitational wave detector that can do this is the space-based <a href="http://www.elisa-ngo.org/">eLISA</a> satellites. (I've also discussed <a href="http://stuver.blogspot.com/search/label/LISA">eLISA and associated drama</a> on this blog previously.) eLISA would be exclusively sensitive to low frequency gravitational wave and would compliment LIGO well: there are many young systems producing low frequency gravitational waves all the time while there are few producing the high frequency death throes that LIGO can detect. Together, LIGO and eLISA will provide a more complete gravitational-wave picture of the life cycle of some of the most energetic, violent objects in the Universe.<br />
<br />
<br />
<b>CONCLUSION</b><br />
<br />
"Gravitational waves" and "gravity waves" are very different entities. However, you may hear us refer to a gravitational wave as a "gravity wave". This is a personal pet peeve of mine (can't you tell?). While I work hard to use the term "gravitational wave" correctly, I am often hesitant to say anything to colleagues I hear using "gravity wave" instead. Watch the NSF documentary <a href="http://www.einsteinsmessengers.org/"><i>Einstein's Messengers</i></a> (also on the "<a href="http://stuver.blogspot.com/p/viewing-fun.html">Viewing Fun</a>" page on this blog) and you will see some highly respected LIGO scientists refer to "gravity waves"; it makes me cringe a little every time but I'm not one to gainsay my betters. Now that you've read this, you'll know what we really mean ;)<br />
<br />
<br />
<b>Read more:</b><br />
<ul>
<li><a href="http://astroengine.com/2009/01/20/gravitational-waves-and-gravity-waves-whats-the-difference/">Another explanation of the difference between gravitational waves and gravity waves</a> (this is correct but a little outdated on its discussion of gravitational waves)</li>
</ul>
stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.com19100 Ligo Road, Walker, LA 70785, USA30.562997199999991 -90.7742061999999815.0409626999999908 -132.08280019999998 56.085031699999988 -49.465612199999981tag:blogger.com,1999:blog-4167914549123471212.post-15874514357585433552013-01-10T20:45:00.002-05:002013-01-18T21:44:24.568-05:00SNEWS and LIGO: Neutrinos Tell of Possible Gravitational WaveWhen I start off a tour at the LIGO Observatory, I usually start by talking about how gravitational waves will open a new window to view the Universe. I've done this so many times that I have the talking point pretty much memorized:<br />
<blockquote class="tr_bq">
"Up until recently, we've only been able to observe the Universe using light and its different forms. <a href="http://en.wikipedia.org/wiki/Visible_light">Visible light</a>, <a href="http://en.wikipedia.org/wiki/X-rays">X-rays</a>, and <a href="http://en.wikipedia.org/wiki/Microwaves">microwaves</a> are just a few different kinds of light and every time we have looked at the Universe in a new way, we discovered something unexpected that revolutionized our understanding of the Universe.<br />
<br />
Well, light has the inconvenient property of being fairly easily <a href="http://en.wikipedia.org/wiki/Absorption_%28electromagnetic_radiation%29">absorbed</a> or <a href="http://en.wikipedia.org/wiki/Reflection_%28physics%29">reflected</a> away from its path. However, the Universe is transparent to gravitational waves; meaning that they can go through matter and come out the other side unchanged. There is no such thing as a gravitational-wave <a href="http://en.wikipedia.org/wiki/Shadow">shadow</a>!"</blockquote>
Note that I start by saying that <i>until recently</i> all of astronomy has used light as its tool. This is because there is another medium that has been used: <a href="http://en.wikipedia.org/wiki/Neutrinos">neutrinos</a>. I've talked a bit about neutrinos previously here, namely when I discussed the <a href="http://stuver.blogspot.com/2012/04/no-faster-than-light-neutrinos.html">debunking of the "faster-than-light neutrino" claim</a> last year and <a href="http://stuver.blogspot.com/2010/10/multi-messenger-astronomy.html">how neutrinos are used in multi-messenger astronomy</a>. Quoting the important part from the multi-messenger astronomy post:<br />
<blockquote class="tr_bq">
"Today, we can do astronomy with means other than light. For example, <a href="http://en.wikipedia.org/wiki/Neutrino">neutrinos</a>.
These are subatomic particles that have no electric charge, have nearly
no mass, travel very near the speed of light and are able to pass
through matter almost undisturbed. However, these properties add up to
make it very hard to detect neutrinos (did you know that there are <b>billions</b>
of neutrinos from the Sun passing through your body every second?!).
Neutrinos are also emitted when a star dies in an explosion called a <a href="http://en.wikipedia.org/wiki/Supernova">supernova</a>.
That means we may observe the optical burst of light AND the neutrinos
from a single supernova. Any time that you can observe the same event
in multiple ways, you almost always learn more than if you only observed
it one way."<br />
<div style="text-align: right;">
<i>- 14 October 2010</i></div>
</blockquote>
What I didn't go into is that LIGO is working to detect gravitational waves from a supernova as well. While we can do this without complementary detections from traditional and neutrino observatories, having that information from them will make it easier for us to find the signal buried under the detector noise that dominates what LIGO records. This is done through the <a href="http://snews.bnl.gov/">Supernova Early Warning System (SNEWS)</a>.<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="http://3.bp.blogspot.com/-G-DpF-zFxaY/UO8m9qptU_I/AAAAAAAAArk/P4qXFk4xci8/s1600/new_snews_logo.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="240" src="http://3.bp.blogspot.com/-G-DpF-zFxaY/UO8m9qptU_I/AAAAAAAAArk/P4qXFk4xci8/s320/new_snews_logo.jpg" width="320" /></a></div>
<br />
<b>SNEWS</b><br />
<br />
Yes, this is pronounced just like you pronounce "snooze". A SNEWS alert is sent out shortly after neutrinos from a supernova (as opposed to neutrinos from the Sun) are detected. Since neutrinos and travel through matter with very little disturbance just like gravitational waves, that means that if we saw neutrinos, there is also a good chance that we may see the gravitational waves from that event. Even more compelling for us in the gravitational wave community is that SNEWS only really expects to see neutrinos from a supernova if it came from within the Milky Way galaxy (or the <a href="http://en.wikipedia.org/wiki/Magellanic_Clouds">Magellanic Clouds</a> that are two small galaxies that orbit the Milky Way). As far as gravitational waves are concerned, that is in our own backyard so any accompanying gravitational waves would likely be large enough for us to detect! (When searching for gravitational waves in general, we expect that almost all of our sources will come from galaxies outside of the Milky Way.)<br />
<br />
<br />
<b>EARLY WARNING SYSTEM?</b><br />
<br />
The reason that the detection of neutrinos is considered an "early warning system" for a supernova is that the processes that produce these neutrinos happen hours to days before the optical explosion that traditional observatories would be able to see. The supernova explosion occurs after the mass of the star collapses in on itself; this is called a core collapse. Neutrinos are normally produced by the <a href="http://en.wikipedia.org/wiki/Nuclear_fusion">nuclear fusions</a> inside the star (our Sun produces MANY all the time), but during the core collapse many more are produced (it is estimated that over 90% of the energy in the collapse is expended as neutrinos). It is also during the core collapse, when so much of the star's mass is in motion, that gravitational waves are produced. If there is a SNEWS alert, that means that there is a higher probability of a gravitational wave detection at that time. <br />
<br />
<br />
<b>WHAT HAPPENS AT LIGO DURING A SNEWS ALERT?</b><br />
<br />
First off, let me say that there has not been a SNEWS alert yet since these supernovae in our galaxy are rare (they happen about every 50 years or so that we are aware of). But if a SNEWS alert comes through while LIGO is looking for gravitational waves, the protocol is quite simple: <b>don't do anything that would cause the quality of the data to be degraded</b>. More specifically, <i>don't create vibrations</i>. Don't walk close to the detector (your footsteps appear to be little earthquakes to the detector), don't leave the site in an automobile (any acceleration by that a car or larger vehicle will create a little wave in the ground that will affect the detector). This has brought up the question of what to do with the FedEx guy if he is on site making a delivery... While we cannot hold anyone against their will, I am sure that he would be asked to stick around for a while. <br />
<br />
This may sound a little harsh, but considering the rarity of these events and what is to be gained, sitting around isn't all that bad!<br />
<br />
<br />
<b>WHAT IS TO BE GAINED?</b><br />
<br />
First, to the traditional astronomy community (telescopes detecting light), it is exceedingly rare to see a supernova from its beginning and doing so can tell astronomers more about what kind of supernova it is (see <a href="http://en.wikipedia.org/wiki/Supernova#Classification">this Wikipedia page</a> for more information about the different types of supernovae).<br />
<br />
Also, if the gravitational waves from the core collapse of a star were to be detected, this will allow us to "see" what went on inside the star - something that can never be done with traditional astronomy. Knowing what goes on inside the star will allow us to use the dying star as a nuclear reactor unlike any we could ever create on Earth. This may be able to tell us more about nuclear physics which could have implications for technology in the future (I have no idea what those may be).<br />
<br />
<br />
<b>NEUTRINOS AND SUPERNOVA IN THE PAST</b><br />
<br />
So far, there are only two detected sources of neutrinos other than those produced by nuclear reactions on Earth: those from the Sun and those from the supernova known as <a href="http://en.wikipedia.org/wiki/SN1987A">SN 1987A</a>.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-BcOuQuccfHQ/UO9s6juEfeI/AAAAAAAAAr4/P0DvG7gzy3o/s1600/Supernova-1987a.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="362" src="http://3.bp.blogspot.com/-BcOuQuccfHQ/UO9s6juEfeI/AAAAAAAAAr4/P0DvG7gzy3o/s400/Supernova-1987a.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span class="description">NASA image of <a href="http://en.wikipedia.org/wiki/SN1987A">1987A supernova</a> remnant near the center. Inset: a close up of the supernova </span>[Source: <a href="http://en.wikipedia.org/wiki/File:Supernova-1987a.jpg">Wikipedia</a>]</td></tr>
</tbody></table>
<br />
SN 1987A happened on 23 February 1987 (hence the name) and was located in the (relatively) nearby <a href="http://en.wikipedia.org/wiki/Large_Magellanic_Cloud">Large Magellanic Cloud</a> and could be seen from the Southern Hemisphere. About 2-3 hours before the star exploded (as seen from Earth), neutrinos were detected at 3 different neutrino detectors. This detection not only was the birth of <a href="http://en.wikipedia.org/wiki/Neutrino_astronomy">neutrino astronomy</a>, but also allowed for the early observation of the light from the supernova.<br />
<br />
Also, this supernova is thought by some to be the instigator of the LIGO concept. This was when Joseph Weber made his claims of the first detection of gravitational waves (which was debunked - but that is a discussion for another blog post). Weber used a method of looking for gravitational waves called a r<a href="http://en.wikipedia.org/wiki/Gravitational-wave_detector#Weber_bars">esonant bar gravitational-wave detector</a> (a.k.a. <a href="http://en.wikipedia.org/wiki/Gravitational-wave_detector#Weber_bars">Weber Bar</a>). Even though there wasn't a gravitational-wave detection, his claims and SN 1987A made scientists begin to consider other way to look for gravitational waves and that the technology needed was within reach. So, that February day in 1987 was also the birth of LIGO in a way! stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comBaton Rouge, LA 70810, USA30.350581299999991 -91.08735509999996830.240967299999991 -91.248716599999966 30.460195299999992 -90.92599359999997tag:blogger.com,1999:blog-4167914549123471212.post-86186853446533677982012-12-31T23:06:00.003-05:002013-01-02T15:01:40.380-05:00Happy New Year!I can't believe how long it's been since I've last blogged - I've had so many ideas of stories to post, but I've also had some life issues that have kept me away. Not to worry! <b><u>My most important resolution for 2013 is to write blog posts a few weeks ahead of time so that I can still post weekly even when life gets in the way. I will be back in full force in 2013!</u></b> Expect posts on <b><u>Thursdays</u></b>, unless there is something timely I want to share before then. I will make sure to post on Twitter when I a new post is available so if you don't follow me already, please follow <a href="https://twitter.com/livingligo">@livingligo</a>.<br />
<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/-j8VGNeaIK-Y/UOSPkAQkR4I/AAAAAAAAApQ/9f-e2vRNazs/s1600/IMAG0027-1.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="258" src="http://4.bp.blogspot.com/-j8VGNeaIK-Y/UOSPkAQkR4I/AAAAAAAAApQ/9f-e2vRNazs/s400/IMAG0027-1.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">This is a smiley face the deicing crew at the <a href="http://www.flypittsburgh.com/">Pittsburgh International Airport</a> made in the snow. As seen through the deicing fluid on the window of my plane on the evening of 29 December 2012.</td></tr>
</tbody></table>
<br />
<br />
<b>2012</b><br />
<br />
This year has been a year of many changes for me. My days as a postdoc have come to an end and I now hold a dual position with Caltech as a scientist at the LIGO Livingston Observatory and as a physics instructor at LSU. It is great being back in the classroom but that is also something that has kept me from posting as much as I would like. It takes a lot of time to create interesting lectures for a class of 150 students and handle all of the class administration myself (office hours, grading, etc.). This semester I am teaching the second semester of physical science (astronomy, chemistry, earth science) and will only have a 30 students. I am very excited about the more personal instruction I will be able to do!<br />
<br />
There have also been many changes at LIGO. When I first started working at the Livingston observatory in 2007, there were about 25-30 people who worked there on a daily basis. Starting with the <a href="https://www.advancedligo.mit.edu/">Advanced LIGO</a> preparations in 2010, we nearly doubled the number of daily staff. Since the installation is well underway, we no longer need to have so many people on site (having too many people on site while we are looking for gravitational waves will cause ground vibrations that will decrease our sensitivity). The parking lots are noticeably less full and it is starting to feel a little lonely even though we still have more people working on site than when I started.<br />
<br />
As far as my personal life is concerned, I'm glad that 2012 is over. It has been full of drama and uncertainty and it is one of the things that have been getting in the way of keeping up with this blog and my career in general. But I wouldn't change a moment of it since I have so many great people around me, at home and at work, who care for me. <br />
<br />
<br />
<b>2013</b><br />
<br />
This coming year will prove to be exciting! The installation of Advanced LIGO should be completed and the first commissioning (use of the detector to fine tune it to its best sensitivity) started. This is always an interesting time when you get to use the detector for the first time and solve novel problems. I will be sure to tell you all about them here! <br />
<br />
I will also continue teaching at LSU. As I mentioned above, I will be teaching the second semester of physical science with about 30 students. I also expect to teach a masters degree class on inquiry learning for in-service teachers this summer (I've done this class twice before with LSU). <br />
<br />
Of course, the most exciting events are usually the unexpected. I look forward to sharing the professional and personal excitement with you here.<br />
<br />
<i>Thank you to all of my readers, followers on Twitter, and those who found me through a search engine! Keep coming back for more!</i><br />
<br />
<b>What are you looking forward to this year?</b>stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comtag:blogger.com,1999:blog-4167914549123471212.post-23454344777723281762012-11-01T22:00:00.001-04:002012-11-02T10:21:20.279-04:00Gravity - The Love Story II: Starstruck!So, where was I when I last posted... Ahh... The great corny love story between two objects bound together by gravity. I started that post asking <a href="http://stuver.blogspot.com/2012/09/gravity-love-story-i-black-holes-are.html">what would happen to the Earth if the Sun were to suddenly become a black hole</a>. Many people think that the Earth would be sucked in because they assume that a black hole will suck everything into it like water going down a drain. But, from careful examination of the <a href="http://stuver.blogspot.com/2012/09/gravity-love-story-i-black-holes-are.html">universal law of gravitation and the story it tells</a>, we see that isn't the case and the Earth will stay in the same orbit that is it now - no closer and no farther away. <br />
<br />
But what about an object flying by a <a href="http://en.wikipedia.org/wiki/Black_hole">black hole</a> (or any other massive object) instead of being in a nice stable orbit (like the Earth is in the <a href="http://stuver.blogspot.com/2012/09/gravity-love-story-i-black-holes-are.html">previous example</a>)? This makes things a little more complicated, so I am going to let go of telling a love story. That being said, there will be more equations here, but like the previous love story post the equations will only serve to help tell the story and we will not be using any numbers.<br />
<br />
<br />
<b>THE FATE OF A COSMIC WANDERER</b><br />
<br />
Instead of looking at the universal gravitation law, we are going to look at how a passing object comes to be in orbit, or not, around another object (this governed by <a href="http://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion">Kepler's laws of planetary motion</a>). To keep things simple, let's assume that the moving object has much, much less mass than the object it's passing (this is so that we can ignore the motion of the big object due to its gravitational attraction to the passing object). Basically, picture something small whizzing through space (I'll call this the <b>small object</b>) that passes by a star or black hole (I'll call this the <b>big object</b>). It is now safe to assume that any motion caused by gravity is going to be seen in the small object.<br />
<br />
<br />
<b>IT'S ALL ABOUT THE SPEED</b><br />
<br />
The one factor that completely determines the fate of the small object is its speed. If this speed is great enough, then the small object will be able to escape the big object, though its speed and direction will have changed. The minimum speed at which the small object will not be captured into an orbit is called the escape velocity:<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
<a href="http://4.bp.blogspot.com/-sfo2EYsvi_U/UJKzX8Jmm6I/AAAAAAAAAes/1oKyAo7YdnY/s1600/escv.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://4.bp.blogspot.com/-sfo2EYsvi_U/UJKzX8Jmm6I/AAAAAAAAAes/1oKyAo7YdnY/s1600/escv.png" /></a></div>
<br />
Here, we see that the escape velocity, v<sub>e</sub>, changes as the square root of 1/distance (1/r) between the objects' centers. That means that the closer the small object is to the big object, the more speed it must have in order not to get caught by it; the farther away, the less speed it needs to escape. 2GM is a constant value and never changes; G being the <a href="http://en.wikipedia.org/wiki/Gravitational_constant">universal gravitational constant</a> and M being the mass of our big object.<br />
<br />
<br />
<b>ORBITS AND ELLIPSES</b><br />
<br />
Any speed less than the escape speed and the small object will be captured by the big object and will likely start orbiting the big object (or collide with it, we'll get to that later). Let's say that we are traveling at a speed less than the escape velocity. Kepler's laws of planetary motion (which are a consequence of gravitation) provide that the shape of the orbit is an <a href="http://en.wikipedia.org/wiki/Ellipse">ellipse</a> (an oval shape). Instead of having one center like a circle does, an ellipse has 2 each called a <a href="http://en.wikipedia.org/wiki/Focus_%28geometry%29">focus</a>. A classic way to draw an ellipse for yourself is to put two pins into a piece of paper, put a loop of string around the pins, place a pen in the loop and pull the loop taut. The shape that you draw doing this is an ellipse:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-av5sFY1HJeE/UJMKMYJVlTI/AAAAAAAAAfA/ozLB_iBl97Q/s1600/Drawing_an_ellipse.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="320" src="http://2.bp.blogspot.com/-av5sFY1HJeE/UJMKMYJVlTI/AAAAAAAAAfA/ozLB_iBl97Q/s320/Drawing_an_ellipse.jpg" width="240" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">[Image from: <a href="http://en.wikipedia.org/wiki/File:Drawing_an_ellipse_via_two_tacks_a_loop_and_a_pen.jpg">Wikipedia</a>]</td></tr>
</tbody></table>
<br />
Here, each pin is a focus. This is what having 2 "centers" means - if you were to draw a shape using this same method but using only one pin, then you would draw a circle (the pin being the true center). When talking about an orbit of a very massive object and much smaller object (like we have in this example, or like the Earth orbiting the Sun), the more massive object will be located at a focus and there isn't anything at the other focus.<br />
<br />
The speed of the object determines the shape of orbit:<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="http://2.bp.blogspot.com/-q25FmFGonwM/UJMOOxXTXSI/AAAAAAAAAfU/3kuS8uTpB4c/s1600/elliptic_v.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://2.bp.blogspot.com/-q25FmFGonwM/UJMOOxXTXSI/AAAAAAAAAfU/3kuS8uTpB4c/s1600/elliptic_v.png" /></a></div>
<br />
Here v is the speed of the orbiting object (which is less than the escape velocity), μ is a constant (G times the mass of the big object), r is the distance from the objects' centers when the velocity is measured, and a is the <a href="http://en.wikipedia.org/wiki/Semi-major_axis">semi-major axis</a> of the ellipse (the distance between the midpoint of the foci and the farthest point of the ellipse). <br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/--e-yfk4b85I/UJMWjfOUiqI/AAAAAAAAAfo/lclR_UAQF2o/s1600/ellipse_axes.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="156" src="http://4.bp.blogspot.com/--e-yfk4b85I/UJMWjfOUiqI/AAAAAAAAAfo/lclR_UAQF2o/s400/ellipse_axes.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">[Image from: <a href="http://en.wikipedia.org/wiki/File:An_image_describing_the_semi-major_and_semi-minor_axis_of_eclipse.png">Wikipedia</a>]</td></tr>
</tbody></table>
<br />
<br />
<b>STARSTRUCK! </b><br />
<br />
Under what conditions does the small object collide with the big object? So far it sounds like the small object is either going to escape the gravitational pull of the big object or start orbiting it. Can a black hole (assuming it's our big object) ever "swallow" anything? Yes, indeed, but only under certain conditions...<br />
<br />
To determine the conditions for an object to be swallowed by a black hole or collide with a star, we need to realize that neither of these objects is a nice point as we have been treating them (well, the <a href="http://en.wikipedia.org/wiki/Gravitational_singularity">singularity </a>inside the black hole is a nice point, but more on that below). Instead, objects occupy a volume and the points we were considering were really the center of <a href="http://en.wikipedia.org/wiki/Center_of_mass">mass of the object</a> (approximately the actual center for a spherical object). So, <u><b>the small object will collide with the big object if the radius of the big object is more than the distance of closest approach of the small object's orbit</b></u>. This distance is called <a href="http://en.wikipedia.org/wiki/Periapsis">periapsis</a> and is the distance along the red line (the semi-major axis) between the ellipse (orbit) and the focus (the big object) in the previous figure. If a star has a radius of this or more, then the small object will slam into it.<br />
<br />
<span style="color: red;"><i><b>NOTE:</b></i></span> This scenario for collision (and the one for merger with a black hole below) <u><b>assumes that the objects only interact through gravity</b></u>. That means that there is no consideration here for other forces like the interactions of the objects' magnetic fields (if they have them) or resistance from the matter and radiation that stars tend to spew out. <br />
<br />
<br />
<b>HUNGRY, HUNGRY, BLACK HOLES</b><br />
<br />
But what about the specific case of a black hole? I mention that there is a point-like singularity in the black hole where all the mass is located. How do we determine the shape of the whole black hole? First, consider why a black hole is called "black"; because the gravity inside of it is so strong that the <a href="http://en.wikipedia.org/wiki/Speed_of_light">speed of light</a> is less than the escape velocity (now you can think of our small object as a <a href="http://en.wikipedia.org/wiki/Photon">photon</a> of light). Since nothing can travel faster than the speed of light, nothing can escape a black hole. So we define the edges of the black hole to be the radius at which the escape velocity equals the speed of light. This radius is called the <a href="http://en.wikipedia.org/wiki/Event_horizon">event horizon</a>. Therefore, <u><b>an object (even a photon) will merge with a black hole when the distance of closest approach of its orbit is equal to or less than the event horizon</b></u>.<br />
<br />
Now that's what I call <i>"starstruck"</i> lovers! Get it? The small object strikes the big object which could be a star... Okay, I know it's lame, but that's why I'm a physicist and not a comedian (though I do try!).<br />
<br />
<br />
<hr />
<br />
<div style="text-align: center;">
<span style="color: #990000;">♥ </span>Speaking of love, happy anniversary to my husband, Derek, who is always nice enough to proofread these posts. We've been together for 16 years, married for 9 and looking forward to many more! <span style="color: #990000;">♥</span></div>
<br />stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comBaton Rouge, LA 70810, USA30.3505813 -91.087355130.295771300000002 -91.1663191 30.4053913 -91.0083911tag:blogger.com,1999:blog-4167914549123471212.post-29581662550530809972012-10-31T17:14:00.000-04:002012-10-31T17:25:32.438-04:00Happy Halloween!Wow! I can't believe how long it has been since I've posted. I've been
horribly busy keeping up with teaching at LSU (and trying my best to
make my lectures interesting), getting my LIGO work done (we are preparing for the 3rd software engineering run for <a href="https://www.advancedligo.mit.edu/">Advanced LIGO</a> [<a href="http://stuver.blogspot.com/2012/01/first-software-engineering-run-for.html">read about the first one here</a>]), and some personal life complications that
we all deal with from time to time. I understand better why the
blessing, "<a href="http://en.wikipedia.org/wiki/May_you_live_in_interesting_times">May you live in interesting times</a>," is more of a curse.<br />
<br />
So, to tide you over until my next full post (tomorrow), here is the feature presentation of the <a href="http://www.ligo-la.caltech.edu/SEC.html">Science Education Center's</a> monthly Science Saturday - Halloween Edition (2011):<br />
<br />
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<iframe allowfullscreen='allowfullscreen' webkitallowfullscreen='webkitallowfullscreen' mozallowfullscreen='mozallowfullscreen' width='320' height='266' src='https://www.youtube.com/embed/he1oCaGytQw?feature=player_embedded' frameborder='0'></iframe></div>
<br />
<br />
Here, William Katzman (Science Education Center Lead) plays a laid back fellow with some paranormal explanations of "spooky phenomena". I play a scientist who explains all of the phenomena in terms of science. Before the day of the presentation, we decided what spooky phenomena we were going to use, but we never rehearsed the show - I'm surprised it turned out so well (if I say so myself)!stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comNicholson Hall, Louisiana State University, Baton Rouge, LA 70802, USA30.4125527 -91.178876830.4108412 -91.181344299999992 30.414264199999998 -91.1764093tag:blogger.com,1999:blog-4167914549123471212.post-25499687133605427892012-09-27T17:54:00.001-04:002012-09-27T20:47:16.588-04:00Gravity - The Love Story I: Black Holes Are Not 'Universal' DrainsThis semester I am teaching a conceptual physics class at LSU that uses minimal mathematics to understand how the Universe works. Yesterday, we covered the chapter on <a href="http://en.wikipedia.org/wiki/Gravity">gravity</a> and my closing question to my students was, <u>"What would happen to the Earth's orbit if the Sun were to become a <a href="http://en.wikipedia.org/wiki/Black_hole">black hole</a> instantly?"</u> Assume that it simply changes in size from what it is now to how big a black hole with the same <a href="http://en.wikipedia.org/wiki/Mass">mass</a> would be and the <a href="http://en.wikipedia.org/wiki/Center_of_mass">center of mass</a> never changes.<br />
<br />
I'm not going to make you wait... <u><b>Nothing would happen to the Earth's orbit!</b></u><br />
<br />
This is one of the most dramatic examples of simply using an equation to tell a story that I have come across. I suspect that much of the drama comes from the <b>misconception</b> that black holes WILL consume EVERYTHING, turning most people's mental picture of a black hole into a universal drain.<br />
<br />
(I know the following analogy is a bit corny, but it makes the point that
equations can tell stories and aren't just recipes to combine numbers
into new numbers...)<br />
<br />
<br />
<b>EQUATIONS TELL A STORY</b><br />
<br />
In order to resolve this misconception, consider <a href="http://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation">Newton's law of universal gravitation</a>:<br />
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<br /></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="http://3.bp.blogspot.com/-P_Ori2KligI/UGSqPeNYYJI/AAAAAAAAAd8/mCYHmARK6y4/s1600/universalG.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://3.bp.blogspot.com/-P_Ori2KligI/UGSqPeNYYJI/AAAAAAAAAd8/mCYHmARK6y4/s1600/universalG.png" /></a></div>
<div class="separator" style="clear: both; text-align: left;">
</div>
Now, don't worry overly that this is an equation because we will be making no calculations. Instead, we are going to use it as a script for a play. This play just so happens to be a love story... <span style="color: #990000;">♥</span><br />
<br />
<br />
<b>THE CAST OF CHARACTERS</b><br />
<br />
On the left side of "=" we don't have a character, but the ending of our story: <i><b>F</b></i>. (This is the gravitational <a href="http://en.wikipedia.org/wiki/Force">force</a> that will be felt between two masses.) We can also think of <i><b>F</b></i> as the attraction between our characters. Therefore, the larger the attraction <i><b>F</b></i>, the better the 'Happily ever after...' ending.<br />
<br />
The story is told by our characters on the right side of "=": <i><b>G</b></i>, <i><b>m<sub>1</sub></b></i>, <i><b>m<sub>2</sub></b></i>, and <i><b>r</b></i>: <br />
<ul>
<li><i><b><a href="http://en.wikipedia.org/wiki/Gravitational_constant">G</a></b></i> is a VERY small constant that is fundamental to the Universe. That is, there is no way to derive its value from any theory, we simply determined this value from measurements. Since <i><b>G</b></i> doesn't change, it is more of a background prop than a character; we
don't need to worry about it since the moral of our story will be the
same with or without it.</li>
<li>Next we have our two lovers: <a href="http://en.wikipedia.org/wiki/Mass">masses</a> <i><b>m<sub>1</sub></b></i> and <i><b>m<sub>2</sub></b></i>. I call them lovers because they are attracted to each other (literally since gravity tends to pull mass together). </li>
<li>Finally, we have our villain, <i><b>r</b></i>, who keeps our lovers apart. (This is the distance between each of our lovers' <a href="http://en.wikipedia.org/wiki/Center_of_mass">center of mass</a>.) </li>
</ul>
That is the complete cast of characters in this story! There are no extras milling around in the background.<br />
<br />
<br />
<b>THE PLOT</b><br />
<br />
When you multiply <i><b>G</b></i>, <i><b>m<sub>1</sub></b></i>, and <i><b>m<sub>2</sub></b></i> together and then divide by <i><b>r</b></i><sup>2</sup> (which is equivalent to <i><b>r</b></i>*<i><b>r</b></i>), you are able to determine the ending to our story which is the attraction (<i><b>F</b></i>) between our lovers. Now we are able to establish some plot points:<br />
<ul>
<li>The more massive either of our lovers (<i><b>m<sub>1</sub></b></i> or <i><b>m<sub>2</sub></b></i>) are, the more they will be attracted to each other.</li>
<li>The farther apart (<i><b>r</b></i>) they are, the less they will be attracted to each other; the bigger the number you divide by, the smaller your result. (The square on <b><i>r</i></b> only serves to make the reduction in attraction between our lovers less even faster. For example, if you double the distance between the lovers, you quarter their attraction.)</li>
</ul>
<br />
<br />
<b>THE SUBPLOT </b><br />
<br />
Now let's take a look at some of the more subtle plot points, specifically the properties that determine the attraction of our lovers (<i><b>m<sub>1</sub></b></i> and <i><b>m<sub>2</sub></b></i>): <br />
<ul>
<li><b>No unrequited love</b>: <i><b>m<sub>1</sub></b></i> and <i><b>m<sub>2</sub></b></i> are always equally attracted to each other. It doesn't matter if one is more massive than the other. </li>
<li><b>Love is blind</b>: There is nothing in our script which describes the size or shape of our lovers. Assuming <i><b>m<sub>1</sub></b></i> and <i><b>m<sub>2</sub></b></i> stay the same distance apart and their masses don't change, they will always be equally attracted to each other. <i><b>m<sub>1</sub></b></i> will love <i><b>m<sub>2</sub></b></i> the same regardless of whether its mass is made up of dense muscle or voluminous blubber. </li>
</ul>
<br />
<br />
<b>"ACTION!"</b><br />
<br />
Now that we have the script to our play, let's see how the ending turns out when we cast the Sun as <i><b>m<sub>1</sub></b></i> and the Earth as <i><b>m<sub>2</sub></b></i>. The scene opens the with Earth orbiting the Sun a fixed distance <i><b>r</b></i> away (this is called an <a href="http://en.wikipedia.org/wiki/Astronomical_unit">astronomical unit</a>, <a href="http://en.wikipedia.org/wiki/Astronomical_unit">AU</a>, and it is about 93 million miles). We sit and watch the Sun and the Earth be attracted to each other, but the villain of distance keeps them apart. In an attempt to overcome our villain, the Sun decides to implode on itself, sucking all of its mass into a ball less than about 3.72 miles across. Now it is a black hole but, according to our script, the Earth felt no change since its love it blind! The mass of the Sun didn't change and its center is still in the same place. Drat, the Sun didn't succeed in increasing its attraction with the Earth!<br />
<br />
<br />
<div style="text-align: center;">
<b><i>~ FIN</i></b> ~</div>
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<br />
<div style="text-align: center;">
<span style="color: #990000;">♥ </span><i>Stay tuned for the next installment of "Gravity - The Love Story"! We will find out what properties our lovers need to have to come together (that is, what properties a mass needs to have to actually get "eaten" by a black hole). </i> <span style="color: #990000;">♥</span></div>
stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.com19100 Ligo Rd, Walker, LA 70785, USA30.5629972 -90.774206230.5612882 -90.776673699999989 30.564706200000003 -90.7717387tag:blogger.com,1999:blog-4167914549123471212.post-17581579469866977132012-09-13T23:11:00.000-04:002013-02-18T02:10:10.624-05:00Q: If Light is Stretched/Compressed by a GW, Why Use Light Inside LIGO?Wow! It's been a while since I've posted... After the start of a new semester (I have 150 students in the class I am teaching at LSU) and <a href="http://en.wikipedia.org/wiki/Hurricane_Isaac_%282012%29">Hurricane Isaac</a> (which shut LIGO Livingston down for almost a week, LSU for 3 days, and left me without power for a while), I am just getting my life back to a somewhat normal routine. I love even the hectic parts of my life, but I've missed writing about gravitational waves here on Living LIGO!<br />
<br />
<br />
<b>Q: IF LIGHT IS STRETCHED/COMPRESSED BY A GRAVITATIONAL WAVE, WHY USE LIGHT INSIDE LIGO?</b><br />
<br />
Today I am addressing a question that many professional physicists fully don't understand! <a href="http://stuver.blogspot.com/2012/08/the-journey-of-gravitational-wave-iii.html">I wrote a little while ago</a> about how light and gravitational waves will stretch out as the Universe expands (this is called <a href="http://en.wikipedia.org/wiki/Redshift">redshift</a>). If an object is coming towards us, its light is compressed (and this is called <a href="http://en.wikipedia.org/wiki/Blueshift">blueshift</a>). Basically, if objects are moving, light and gravitational waves will experience a <a href="http://en.wikipedia.org/wiki/Doppler_effect">Doppler effect</a>. <a href="http://stuver.blogspot.com/2012/06/q-what-would-gravitational-wave-feel.html">I have also written </a>about how a passing gravitational wave will stretch and compress space in perpendicular directions. When you put these two facts together, you come to the conclusion that the light inside the arms of LIGO is also be stretched and compressed by a gravitational wave. <i><b>So, how can we use this light to measure gravitational waves when the light itself is affected by the gravitational wave?</b></i><br />
<br />
Like I suggested earlier, this is not obvious upon first inspection. The apparent paradox arises from thinking of laser light as a ruler. When you think of light, you usually think of it as a wave (which it is, but <a href="http://en.wikipedia.org/wiki/Wave-particle_duality">light is also a particle</a> - however that isn't relevant to this discussion). Waves have a <a href="http://en.wikipedia.org/wiki/Wavelength">wavelength</a> -- the distance between each successive wave:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-QLTW6qbUb2Q/UFI74PKDgaI/AAAAAAAAAcc/vb78n7h7yVY/s1600/wavelength.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="222" src="http://1.bp.blogspot.com/-QLTW6qbUb2Q/UFI74PKDgaI/AAAAAAAAAcc/vb78n7h7yVY/s320/wavelength.png" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Illustration of wavelength (represented by λ) measured from various parts of a wave. [Source: <a href="http://en.wikipedia.org/wiki/File:Sine_wavelength.svg">Wikipedia</a>]</td></tr>
</tbody></table>
<br />
A passing gravitational wave will expand and compress space-time and the wavelength of the light we are using to measure gravitational waves is itself affected by the gravitational wave. Since LIGO and detectors like it effectively measure the length of its arms and compares them to each other, <i>how can we rely on light to measure any length changes from a passing gravitational wave? </i><br />
<br />
The solution begins to become clear when you start thinking of the laser light as a <b>clock</b> instead of a ruler. When the light comes out of the laser, there is a fixed time between each crest of the wave (this is called the <a href="http://en.wikipedia.org/wiki/Period_%28physics%29">period</a> of the wave). Let's label each crest as 'tick' (like a clock). Our laser (labeled 'Laser' in the image below) is very stable in that it produces a very consistent wavelength of 1064 nm (near-<a href="http://en.wikipedia.org/wiki/Infrared">infrared </a>light). Because the <a href="http://en.wikipedia.org/wiki/Speed_of_light">speed of light</a> is constant no matter how you measure it, that means that there are almost 282 trillion (2.817 x 10<sup>14</sup>) 'ticks' every second. This light is then split into two equal parts (at the 'Beam Splitter' in the image below), one for each arm.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-GFquOXqODvs/UFJAizhHfqI/AAAAAAAAAcw/sjxujKAPUAI/s1600/IFO.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="195" src="http://3.bp.blogspot.com/-GFquOXqODvs/UFJAizhHfqI/AAAAAAAAAcw/sjxujKAPUAI/s320/IFO.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Basic diagram of the LIGO detectors.</td></tr>
</tbody></table>
<br />
Since different things can happen to the light once it is in the arms, let's reference the beam splitter for making length measurements (i.e., let the beam splitter stay in the same place while the gravitational wave alternates squishing and stretching the arms). A real gravitational wave will cause one arm to shorten and the other to lengthen. This will also cause the laser wavelength in the shortened arm to decrease (blueshift) and the wavelength in the lengthened arm to increase (redshift). But there is nothing in the detector that measures wavelength. What it really measures is the shift in the arrival time of each 'tick' of the wavelength crests. If the arms stay the same length (no gravitational wave), then the 'ticks' of the laser light come back to the beam splitter at the same time and produces destructive interference where we measure the light (labeled 'Photodetector' in the image above). If a gravitational wave causes the length of the arms to change and
shifts where the 'ticks' of the laser light occur, the two light
beams will no longer return to the beam splitter at the same time. <u><b>It is this "out of sync" arrival time of the crests of the laser light that produces the interference patter we utilize to detect gravitational waves</b></u> - we couldn't care less about the actual wavelength of the light (other than it was consistent going into the detector).<br />
<br />
<br />
<b>READ MORE FROM OTHER LIGO SCIENTISTS:</b><br />
<br />
A wonderful, concise summary on why light can be used in gravitational wave detectors like LIGO has been published in <i>American Scientist</i> <a href="http://www.americanscientist.org/issues/pub/2004/11/wavy-gravy">here</a>. The author, <a href="http://www2.physics.umd.edu/%7Epshawhan/">Peter Shawhan</a>, is an associate professor at the University of Maryland, College Park.<br />
<br />
There is also an article in the American Journal of Physics (vol. 65, issue 6, pp. 501-505) titled "<span style="font-size: small;">If light waves are stretched by gravitational waves, how can we use light as a ruler to detect gravitational waves?</span>" This is a more technical article by <a href="http://www.gravity.phy.syr.edu/group_members/faculty/peter_saulson.html">Peter Saulson</a> who is a professor at Syracuse University. stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comBaton Rouge, LA 70810, USA30.3505813 -91.087355130.295771300000002 -91.1663191 30.4053913 -91.0083911tag:blogger.com,1999:blog-4167914549123471212.post-62741674592882431472012-08-23T18:46:00.002-04:002012-08-23T22:36:29.455-04:00My New Jobs and Working in Academia <b>THE NEW JOBS </b><br />
<br />
I've talked before about my current position as a <a href="http://en.wikipedia.org/wiki/Postdoctoral_research">postdoc</a> (short for postdoctoral scholar/researcher/fellow/etc.). This is a temporary position very much like a medical doctor's residency. I've held this position for the past 5 years and I've loved it, so much so that I managed to land myself a more permanent position, or I should say positions since I now have 2 jobs.<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="http://2.bp.blogspot.com/-lY6Yu2aQvUw/UDattSUOssI/AAAAAAAAAbY/Xx3y1_aw2nw/s1600/Caltech+logo.png" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="169" src="http://2.bp.blogspot.com/-lY6Yu2aQvUw/UDattSUOssI/AAAAAAAAAbY/Xx3y1_aw2nw/s200/Caltech+logo.png" width="200" /></a></div>
My first job that will be replacing my postdoc (which is up at the end of the month) is "Data Analysis and EPO Scientist" for Caltech but working at the LIGO Livingston Observatory (EPO stands for Education and Public Outreach). This is a half-time position that will allow me to continue my LIGO research and continue to perform outreach. Basically, this new scientist job at LIGO will let me to keep doing what I've been doing for the last 5 years.<br />
<br />
<a href="http://4.bp.blogspot.com/-ITsukhaarVY/UDavWQpvYyI/AAAAAAAAAbo/lLIpt-wiPFc/s1600/LSU-logo.jpg" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" height="150" src="http://4.bp.blogspot.com/-ITsukhaarVY/UDavWQpvYyI/AAAAAAAAAbo/lLIpt-wiPFc/s200/LSU-logo.jpg" width="200" /></a>My second job is an instructor position in the LSU physics department. This semester I am teaching conceptual physics (<a href="http://www.phys.lsu.edu/newwebsite/graduate/courseoffer2.html#phsc1001">PHSC 1001: Physical Science</a>) which is sometimes referred to as "physics for poets". I am especially excited about teaching the class at LSU because many of the students are future teachers themselves. I've taught the equivalent course to this while I was at Penn State (<a href="http://bulletins.psu.edu/undergrad/courses/P/PHYS/001">PHYS 001: The Science of Physics</a>). This was the one course I had complete control over while I was at Penn State: including text book selection, lecture & exam creation, etc. I picked this class because it is hard to teach. Through my previous teaching experience, I discovered that the less math you use in a physics class, the harder it is to teach. Calculus-based physics is MUCH easier to teach than algebra-based; not because the students in the calculus-based physics class are smarter (which isn't true), but because a teacher can use math as a crutch and not have to truly articulate concepts. <br />
<br />
<br />
<b>THE GOOD AND THE BAD</b><br />
<br />
I am really thrilled about my jobs. Not only do I have a job (with benefits) in this economic climate, but it is in my field and doing what I love to do. I am also back in the classroom which I missed (but loved the work in outreach I've been doing). I get to continue doing to LIGO research.<br />
<br />
In a sense, I have a very non-traditional "professorship" since I get to teach and do research. The reason this isn't really a professorship is that I do not have the ability to earn <a href="http://en.wikipedia.org/wiki/Tenure#Academic_tenure">tenure</a>. In academia, after a certain amount of time (usually 7 years) you are eligible for a promotion that makes you a permanent member of the faculty at the school. In higher education, the evaluation criteria usually include the quality of your research (usually measured on the amount of grants you obtained and papers that you published), your teaching, and your service to the school and the profession. At <a href="http://en.wikipedia.org/wiki/Research_I_university">very big research schools</a>, much more weight is placed on research; in smaller <a href="http://en.wikipedia.org/wiki/Liberal_arts_college">liberal arts colleges</a>, teaching is often more important. The fact that I am in a non-tenure track position is good in that I don't have to worry about obtaining my own research funds or publish stacks of papers and it is bad in that I am never going to have the security that tenure could bring me. Of course, I have the option of leaving my current positions in the future and finding a tenure-track job (which isn't easy to do these days).<br />
<br />
Another good aspect about my split position is that it think it is pretty hard to get laid off from two different jobs at the same time. I guess that's a kind of job security... I may not have tenure but it will be hard for me to be completely unemployed.<br />
<br />
Ultimately, I am thrilled that two different universities are willing to claim me and I still get to do what I love... It doesn't get much better than that!stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.com19100 Ligo Rd, Walker, LA 70785, USA30.5629972 -90.774206230.5612882 -90.776673699999989 30.564706200000003 -90.7717387tag:blogger.com,1999:blog-4167914549123471212.post-20474563837402986772012-08-10T13:02:00.000-04:002013-03-21T10:51:38.833-04:00The Journey of a Gravitational Wave III: GWs Stretch Out<i>What happens to a gravitational wave between when it is produced and
when LIGO can detect it? It turns out not much, which makes it a key
new medium in which to observe the Universe!</i><br />
<br />
<u>Today I will be discussing how a gravitational wave can get stretched during its journey to Earth</u>. Previously, we have discussed <a href="http://stuver.blogspot.com/2012/07/the-journey-of-gravitational-wave-ii-gw.html">how gravitational waves can be bent away from a straight path</a> and <a href="http://stuver.blogspot.com/2012/07/journey-of-gravitational-wave-i-gws.html">how things cannot absorb or reflect a gravitational wave</a>.
<br />
<br />
<br />
<b>THE DOPPLER EFFECT</b><br />
<br />
If you have ever been passed by an ambulance or police car with its sirens on, then you likely noticed that as the sound from the siren approached you, the tone was higher than when the siren passed you. This is due to something called the <a href="http://en.wikipedia.org/wiki/Doppler_effect">Doppler effect</a>. As the source of a sound is moving toward toward you, the distance between the sound wave's crests (<a href="http://en.wikipedia.org/wiki/Wavelength">wavelength</a>) are compressed, resulting in a higher frequency. We hear higher frequencies as higher tones. Conversely, when the source of a sound is moving away from you, the sounds wave's crests are stretched apart resulting in a lower frequency and a lower tone. Consider the following animated example:<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
</div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://upload.wikimedia.org/wikipedia/commons/9/90/Dopplerfrequenz.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="80" src="http://upload.wikimedia.org/wikipedia/commons/9/90/Dopplerfrequenz.gif" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Animated example of the Doppler effect: how motion and cause the wavelength of sound to be affected.<br />
[Image from <a href="http://en.wikipedia.org/wiki/File:Dopplerfrequenz.gif">Wikipedia</a>]</td></tr>
</tbody></table>
<br />
In the beginning of this animation, the car is not moving and the sound waves have the same wavelength both in front and behind the car. Once it starts moving forward (to the left), the sound waves in front of the car are closer together and the sound waves behind the car are farther apart. This results in us hearing a higher tone when you are in front of the car and a lower tone when you are behind the car.<br />
<br />
<br />
<b>COSMOLOGICAL <span style="color: #cc0000;">REDSHIFT</span></b><br />
<br />
This Doppler effect can also affect the wavelength of light <i>and of a gravitational wave</i><b> </b>depending on the motion of the object creating the waves. First, let's think about what happens to light. As the source moves toward you, the wavelength of the light will get shorter. Since we can't hear light, instead of hearing a higher tone, we will see the light to be shifted toward the blue end of the spectrum (where the shortest wavelengths we can see are). This is called <a href="http://en.wikipedia.org/wiki/Blueshift">blueshift</a>. For a source moving away from us, the wavelengths would be longer and we would see the light shifted toward the red end of the spectrum (where the longest wavelengths we can see are). This is called <a href="http://en.wikipedia.org/wiki/Redshift">redshift</a>. <br />
<br />
We can measure this cosmological Doppler effect by measuring the spectral signatures of stars. Below is an example of such a spectral signature. Stars give off almost every color of light, but there are particular colors that get absorbed by different elements before that light can make it to Earth. Those absorbed colors show up as dark lines in an otherwise complete spectrum of colors:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-ptegyOece9s/UBmH28wAErI/AAAAAAAAAak/UlYaJiXHFrw/s1600/Redshift.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="320" src="http://1.bp.blogspot.com/-ptegyOece9s/UBmH28wAErI/AAAAAAAAAak/UlYaJiXHFrw/s320/Redshift.png" width="181" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The optical spectrum from our Sun (left) compared to the optical spectrum of a supercluster of galaxies (right). Note that there are similar <a href="http://en.wikipedia.org/wiki/Absorption_line">dark lines</a> (from <a href="http://www.blogger.com/goog_758759115">absorption of those wavelengths</a><a href="http://en.wikipedia.org/wiki/Absorption_line"> by different chemical elements</a>), but the lines on the right are shifted toward the red end of the spectrum. This phenomena is called "<a href="http://en.wikipedia.org/wiki/Redshift">redshift</a>" because of this. [Source: <a href="http://en.wikipedia.org/wiki/File:Redshift.png">Wikipedia</a>]</td></tr>
</tbody></table>
<br />
The spectrum to the left is what we observe from our local star, the Sun. The spectrum on the right is from a distant cluster of galaxies (containing many stars). Note that the spacing of the dark lines is essentially the same, just shifted toward the red end of the spectrum (this is highlighted by the arrows). That means that this cluster of galaxies is moving away from us. Just about everything (but not quite) in the Universe shows this redshift which implies that <u><b>the Universe is expanding</b></u>! (There is more than one cause of redshift, but we will only be discussing the redshift due to the expanding Universe in this blog post.)<br />
<br />
Redshift is measured by the change in wavelength of light (or a gravitational wave) divided by the wavelength of light if the source wasn't moving. For the spectrum example here, this would be the amount the color of the light changed (the difference between the right and the left side) divided by its original color (the left side). The redshift is a result of the Doppler effect; it can also be used to measure an object's velocity. To do that, we need to determine the proportionality constant between redshift and velocity. This constant is known as the Hubble constant, H (named after <a href="http://en.wikipedia.org/wiki/Edwin_Hubble">Edwin Hubble</a> who first determined this relationship). The best estimate of this constant is currently:<br />
<br />
<div style="text-align: center;">
<b>H = <strike>71.0 ± 2.5 <a href="http://en.wikipedia.org/wiki/Km">km</a>/s/<a href="http://en.wikipedia.org/wiki/Parsec">Mpc</a></strike></b><br />
<b> 67.2 </b><b>± 1.2 </b><b><a href="http://en.wikipedia.org/wiki/Km">km</a>/s/<a href="http://en.wikipedia.org/wiki/Parsec">Mpc</a></b><br />
(revised on 20 March 2013 with the parameters released by <a href="http://en.wikipedia.org/wiki/Planck_%28spacecraft%29">Planck</a>)<b> </b></div>
<br />
This means that for every <a href="http://en.wikipedia.org/wiki/Light-year">light-year</a> away an object is, its velocity away from us increases by about 257 feet/hour. (This may not sound like much, but a light-year is really a very small distance in the Universe; our own galaxy is about <b><i>110,000 light-years</i></b> across!) This expansion is believed to have originated with the <a href="http://en.wikipedia.org/wiki/Big_bang">Big Bang</a>. So, will the Universe expand forever? Will it slow to a stop? Will it stop expanding and start shrinking until everything is a compact ball again (this is called the <a href="http://en.wikipedia.org/wiki/Big_Crunch">Big Crunch</a>)? From current observations, the <a href="http://en.wikipedia.org/wiki/Ultimate_fate_of_the_universe">ultimate fate of the Universe</a> appears to be an eternal slowing expansion which will cause all of the energy to be evenly distributed throughout this even larger Universe (compared to now). That means that there won't be enough energy in any one place to make anything happen (all events in the Universe need an imbalance in energy). This is called the <a href="http://en.wikipedia.org/wiki/Ultimate_fate_of_the_universe">Big Freeze or the heat death of the Universe</a>. However, more observations (especially of things like dark matter and dark energy) of our Universe are needed before we can be sure of the Universe's future.<br />
<br />
<br />
<div style="color: blue;">
<b>BLUESHIFT</b></div>
<br />
There are a <i>few</i> things in our Universe that are moving towards us and therefore have a <a href="http://en.wikipedia.org/wiki/Blueshift">blueshift</a>. Of most note is the <a href="http://en.wikipedia.org/wiki/Andromeda_Galaxy">Andromeda Galaxy</a> which is moving towards us at about 300,000 meters/s (671,801 mph). This is because our Milky Way Galaxy and the Andromeda Galaxy are gravitationally bound to each other; this means that the gravitational attractions between these two galaxies are greater than the expansion of the Universe. In the future, our two galaxies will collide, but not for an estimated 4.5 billion years. This is also about the time the that our <a href="http://en.wikipedia.org/wiki/Sun">Sun</a> will become a <a href="http://en.wikipedia.org/wiki/Red_giant">red giant</a> and all life on Earth will be extinct by then anyway! I wouldn't stress about it if I were you :P<br />
<br />
Also, portions of rotating galaxies can be blueshifted. In this case, the side that is rotating toward us will be blueshifted and the part that is rotating away from us will be redshifted.<br />
<br />
<br />
<b>GRAVITATIONAL WAVES AND REDSHIFT</b><br />
<br />
Just like redshift stretches out the wavelength of light, the expansion of the Universe will also stretch out the wavelength of a gravitational wave during its journey to Earth. <a href="http://stuver.blogspot.com/2012/06/what-do-gravitational-waves-sound-like.html">In a previous post, I discussed what gravitational waves would sound like</a> if you put their signal through a speaker (remember: gravitational waves don't make sound!). So, I decided I wanted to hear what the change in the sound of a gravitational wave is due to different amounts of redshift. I did the calculations, generated the sounds, and assembled them into the video below for your viewing pleasure:<br />
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<iframe allowfullscreen='allowfullscreen' webkitallowfullscreen='webkitallowfullscreen' mozallowfullscreen='mozallowfullscreen' width='320' height='266' src='https://www.youtube.com/embed/054p3Ur-gT0?feature=player_embedded' frameborder='0'></iframe></div>
<br />
So, how can we make use of the redshifting of a gravitational wave to learn more about our Universe? Well, most astronomers and physicists don't believe that the rate of expansion of the Universe (the Hubble constant, H, above) has been the same since the Big Bang. Particularly, there is a period believed to have existed in the past history of the Universe called <a href="http://en.wikipedia.org/wiki/Inflation_%28cosmology%29">inflation</a> which is a time of rapid expansion. From a certain kind gravitational wave source, we will be able to measure the Hubble constant around the neighborhood of the source. This will be a direct probe of how the expansion of the Universe (the Hubble constant) has changed through the history of the Universe because observing objects in the distance is the same as observing them as they were in the past (e.g. observing an object 1 light-year away is the same as observing it as it was a year ago since light and gravitational waves travel at the speed of light - at least gravitational waves are expected to travel at the speed of light!).stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.com19100 Ligo Rd, Walker, LA 70785, USA30.5629972 -90.774206230.5612882 -90.776673699999989 30.564706200000003 -90.7717387tag:blogger.com,1999:blog-4167914549123471212.post-34097855340366696292012-07-26T23:58:00.001-04:002012-07-27T00:24:38.871-04:00The Journey of a Gravitational Wave II: GWs Get Bent<i>What happens to a gravitational wave between when it is produced and
when LIGO can detect it? It turns out not much, which makes it a key
new medium in which to observe the Universe!</i><br />
<br />
Last week, I began discussing what happens to a gravitational wave as it makes its way from its source to Earth; <a href="http://stuver.blogspot.com/2012/07/journey-of-gravitational-wave-i-gws.html">specifically that gravitational wave can travel through matter and come out the other side unchanged</a>!
<u>Today's post talks about how the gravitational effects of other masses
in the Universe can deflect the gravitational wave from its otherwise
straight path</u>. <br />
<br />
<br />
<b>GRAVITATIONAL LENSING</b><br />
<br />
Let's think again about what happens to light on its way to Earth. We know from the <a href="http://stuver.blogspot.com/2012/07/journey-of-gravitational-wave-i-gws.html">last post</a>
that any matter light comes into contact with will reflect or absorb at
least part of the light. There is also another effect called <a href="http://en.wikipedia.org/wiki/Gravitational_lens">gravitational lensing</a>
that causes light to bend around massive objects due to the massive
object's gravitational influence. This is caused by light following its
natural path on curved spacetime (or light being bent by a
gravitational field since we've <a href="http://stuver.blogspot.com/2012/05/q-what-is-gravitational-wave.html">previously established</a>
that the curvature of spacetime is a representation of the strength of
the gravitational field there). The first thing that pops into my mind
that illustrates something following its natural path on a curved
surface is <a href="http://en.wikipedia.org/wiki/Miniature_golf">miniature golf</a>:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://2.bp.blogspot.com/-2cHWnUlZK1Y/UBFnJ1tJQFI/AAAAAAAAAZY/3Z2TjRNGLTc/s1600/minigolf.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" height="225" src="http://2.bp.blogspot.com/-2cHWnUlZK1Y/UBFnJ1tJQFI/AAAAAAAAAZY/3Z2TjRNGLTc/s320/minigolf.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">This is hole 13 at <a href="http://nocache.homestead.com/maxovideoatl/Safariminigolf.html">Safari Mini Golf</a> in Vero Beach, FL. This image is taken from a review of this course and can be read <a href="http://www.floridaminiaturegolfreview.com/reviews/safari-mini-golf-vero-beach-review/">here</a>.</td></tr>
</tbody></table>
Consider
the example hole in the above image. After you get your ball past the
three bumps, there is a wonderful bowl-like curved portion behind the
target hole (if you look very closely, you can see the hole directly after the last bump and in the center). If you hit your ball into this area, the ball's trajectory
will change from a straight path to a curved one. If your ball begins
its path on the left side of the bowl, it will curve right; if your ball
enters the bowl from the right, it will curve left. The same thing
happens for light and gravitational waves that pass by a massive enough
object to cause a significant depression in spacetime (i.e. a strong gravitational
field):<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-cQKPOurFnbE/UBFopRGTzuI/AAAAAAAAAZg/AUTaS6qjaYc/s1600/relativity_light_bending.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" height="320" src="http://3.bp.blogspot.com/-cQKPOurFnbE/UBFopRGTzuI/AAAAAAAAAZg/AUTaS6qjaYc/s320/relativity_light_bending.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The bending of light from a star that is really behind the Sun but appears to be to the side of the Sun. <br />
[Credit: <a href="http://scienceblogs.com/startswithabang/">Ethan Siegel</a> of Lewis & Clark College, OR]</td></tr>
</tbody></table>
<br />
The
the light from a star, galaxy, or other source travels through the
depression in spacetime made by a nearby massive object (in the image
above it is the Sun). The path that light takes is curved just like
the golf ball in the miniature golf example above. But our brains are
wired to assume that any light that enters our eyes has come to us in a
straight line (which is how light usually travels) so we perceive the
location of the source to be directly behind where it appears to be.
Therefore, while the star is really behind the Sun (at point A in the
image above), it appears to us to be to the side of the Sun (at point
B). This bending effect is called gravitational lensing and it applies to gravitational waves just like it does to light.<br />
<br />
<br />
<b>KINDS OF GRAVITATIONAL LENSING</b><br />
<br />
The
example of gravitational lensing given above was <a href="http://en.wikipedia.org/wiki/Tests_of_general_relativity#Deflection_of_light_by_the_Sun">one of the first observational proofs that Einstein's general relativity</a> was correct.
Before relativity, there was already a prediction of the bending of light due to
<a href="http://en.wikipedia.org/wiki/Newtonian_gravity">Newtonian gravity</a> (what we use in our everyday life) but Einstein
predicted the bending effect should be twice that predicted without
relativity. <a href="http://en.wikipedia.org/wiki/Solar_eclipse_of_May_29,_1919">In 1919, there was a total eclipse of the Sun</a> which would
allow those stars that are near the Sun to become visible. Images of
the eclipse were taken and it was seen that the shift in the position of
stars near the Sun was indeed twice that of the shift predicted by
Newtonian gravity.<br />
<br />
There are also kinds of lensing that produce much more dramatic
effects than shifting the position of stars! Things like large galaxies and clusters
of galaxies can cause the light from objects behind them to be split up
to form multiple, separate, and complete images. <br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-v-TaviWzj3o/UBHzbilFazI/AAAAAAAAAZ0/R74_ykDlebI/s1600/lens-annotated.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" height="240" src="http://1.bp.blogspot.com/-v-TaviWzj3o/UBHzbilFazI/AAAAAAAAAZ0/R74_ykDlebI/s320/lens-annotated.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">[Image from <a href="http://www.nasa.gov/multimedia/imagegallery/image_feature_575.html">NASA</a>]</td></tr>
</tbody></table>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
The image above shows gravitational lensing of a
quasar and a galaxy by a distant galaxy cluster SDSS J1004+4112 (SDSS
indicates that it was discovered by the <a href="http://en.wikipedia.org/wiki/Sloan_Digital_Sky_Survey">Sloan Digital Sky Survey</a>). Each image of the <a href="http://en.wikipedia.org/wiki/Quasar">quasar</a> is of the same single object; the same is true of the galaxy! <br />
<br />
You may notice that each of the images are a little different
from each other. This is due to the distortion that a gravitational
lens can cause. This effect is illustrated well in the simulation below
of a black hole creating a gravitational lens as it passes in front of a
galaxy:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/--t07xGYr_nw/UBH1mrsSd2I/AAAAAAAAAZ8/QxxpiAyheOk/s1600/lens-simulation.gif" style="margin-left: auto; margin-right: auto;"><img border="0" src="http://3.bp.blogspot.com/--t07xGYr_nw/UBH1mrsSd2I/AAAAAAAAAZ8/QxxpiAyheOk/s1600/lens-simulation.gif" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">[Image from <a href="http://en.wikipedia.org/wiki/File:Black_hole_lensing_web.gif">Wikipedia</a>]</td></tr>
</tbody></table>
<br />
Note the circular distortion of the
light from the galaxy as the black hole passes by. When the black hole
is directly in front of the galaxy, there is a circular halo of lensed
light around it. This halo called an <a href="http://en.wikipedia.org/wiki/Einstein_ring">Einstein Ring</a> can can be caused by any extremely massive object (black hole, galaxy, galaxy cluster, etc.).<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-ObzNV9IgP1o/UBH6VcUs3yI/AAAAAAAAAaQ/DQSj7ukDJB0/s1600/Einstein_Rings.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" height="256" src="http://1.bp.blogspot.com/-ObzNV9IgP1o/UBH6VcUs3yI/AAAAAAAAAaQ/DQSj7ukDJB0/s320/Einstein_Rings.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">[Image credited within the image and retrieved from <a href="http://en.wikipedia.org/wiki/File:Einstein_Rings.jpg">Wikipedia</a>.]</td></tr>
</tbody></table>
<br />
<br />
<b>HOW LENSING AFFECTS THE SEARCH FOR GRAVITATIONAL WAVES</b><br />
<br />
Gravitational
lensing affects both light and gravitational waves. This produces
spectacular images of objects using light, but LIGO will not produce images and the
sources that produce gravitational waves are more point-like (a black
hole, a star exploding, etc.) than large scale objects (like galaxies which are thousands of <a href="http://en.wikipedia.org/wiki/Light_year">light-years</a> across).
The effect that will most likely be seen in gravitational waves is
their focusing; the bending of gravitational waves can produce more
intense gravitational waves from the lensed source (similar to a magnifying glass focusing light to a smaller point). <a href="http://iopscience.iop.org/1538-4357/517/1/L31/fulltext/985903.text.html">This paper</a>
suggests that the galactic center of the <a href="http://en.wikipedia.org/wiki/Milky_way">Milky Way</a> could increase the
intensity of a source in our galaxy (bur behind the galactic center) up
to 4000x. Also, if a gravitational wave is emitted from a galaxy that
has multiple images from lensing, then that gravitational wave will come
from each image!<br />
<br />
However, most sources will not have appreciable
lensing. While this is something we will always need to consider while
conducting gravitational-wave astronomy, it isn't something that is
likely to change the information contained on the
gravitational wave noticeably (and that's a good thing)!stuverhttp://www.blogger.com/profile/15411280527486674142noreply@blogger.comBaton Rouge, LA 70810, USA30.3505813 -91.087355130.295771300000002 -91.1663191 30.4053913 -91.0083911