Methods of Detecting Gravitational Waves I: Resonant-Mass Detectors

As 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...

WEBER BARS

In 1966, Joseph Weber 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 resonant frequency, for Weber's bars was 1660 Hz (cycles per second).

Weber working on one of his bars at the University of Maryland, c. 1965.

The way these bars are be used to detect gravitational waves involves the phenomenon of sympathetic resonance.  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).

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:

This stretching and compressing is the vibration that makes the bar 'ring'.

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 piezoelectric crystal) 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.

But just like there are many things other than gravitational waves that can cause noise in the data that LIGO collects, there were many other things that could cause the motion of Weber's bars.  Even the vibration of the aluminum atoms in the bar due to their temperature (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 strain (which is defined to be the change in length divided by the original length of an object) of about 10^-16.  To give this scale some reference, a "large" gravitational wave to LIGO would produce a strain of about 10^-21 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...

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 (SN1987A).

One of Weber's original bars on display at the LIGO Hanford Observatory in August 2004.

There are many 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!


MODERN BARS

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.


COMPARISON TO DETECTORS LIKE LIGO

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.


THE DETECTORS RIGHT NOW

If you are interested in the operational state of gravitational-wave detectors (including resonant-mass detectors) click here.  AURIGA and NAUTILUS are both bar detectors while GEO 600, LIGO, and Virgo are interferometers.

SNEWS and LIGO: Neutrinos Tell of Possible Gravitational Wave

When 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:

"Up until recently, we've only been able to observe the Universe using light and its different forms.  Visible light, X-rays, and microwaves 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.

Well, light has the inconvenient property of being fairly easily absorbed or reflected 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 shadow!"

Note that I start by saying that until recently all of astronomy has used light as its tool.  This is because there is another medium that has been used: neutrinos.  I've talked a bit about neutrinos previously here, namely when I discussed the debunking of the "faster-than-light neutrino" claim last year and how neutrinos are used in multi-messenger astronomy.  Quoting the important part from the multi-messenger astronomy post:

"Today, we can do astronomy with means other than light.  For example, neutrinos.  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 billions of neutrinos from the Sun passing through your body every second?!).  Neutrinos are also emitted when a star dies in an explosion called a supernova.  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."

- 14 October 2010

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 Supernova Early Warning System (SNEWS).

SNEWS

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 Magellanic Clouds 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.)


EARLY WARNING SYSTEM?

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 nuclear fusions 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.


WHAT HAPPENS AT LIGO DURING A SNEWS ALERT?

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: don't do anything that would cause the quality of the data to be degraded.  More specifically, don't create vibrations.  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. 

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!


WHAT IS TO BE GAINED?

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 this Wikipedia page for more information about the different types of supernovae).

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).


NEUTRINOS AND SUPERNOVA IN THE PAST

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 SN 1987A.

NASA image of 1987A supernova remnant near the center.  Inset: a close up of the supernova  [Source: Wikipedia]

SN 1987A happened on 23 February 1987 (hence the name) and was located in the (relatively) nearby Large Magellanic Cloud 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 neutrino astronomy, but also allowed for the early observation of the light from the supernova.

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 resonant bar gravitational-wave detector (a.k.a. Weber Bar).  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!

Academic Genealogy

I think that I have mentioned in other posts in this blog that one of my hobbies is genealogy.  I am planning to write more on my family history someday (it's always fun to find a great-grandfather in the state penitentiary when doing a census search) but I wanted to talk a little today about my academic genealogy. 

When earning an graduate degree in an academic field, one normally had an advisor that mentors the students in their research.  So, you can trace back through time who your advisor's advisor was and so on.  Normally, a modern student has only one advisor unless their research is interdisciplinary or other reasons.  Therefore, unlike a normal family tree where each child has a mother and a father, an academic genealogy doesn't branch as much.

I have done some research in the past on my academic genealogy.  My doctoral advisor was Lee Samuel Finn at Penn State and his advisor was Kip Thorne at Caltech.  On my own, I was able to trace my academic genealogy back about 10 'generations'.

Recently, I found the Mathematics Genealogy Project (MGP).  This work by North Dakota State University tracks the academic genealogy of mathematicians both their 'ancestors' and their 'descendants'.  Lucky for me, physics is closely related to mathematics (after all, Newton did pioneer calculus in order to do his physics) and my immediate academic family is documented in the MGP.  I found my advisor and started moving back through my ancestors.  It was amazing going back in time like this!  My academic genealogy goes back through 7 centuries to the High Middle Ages (essentially the founding of universities in Europe) and spans the fields of physics, astronomy, mathematics, chemistry, biology, medicine, philosophy and theology.  Before my academic great-grandfather all my 'ancestors' were educated in Europe, mostly in Germany, Austria, France and Italy.  And while this is not at all surprising, I am the only female in the tree (if you click on the poster sized image below, it will be a 6 MB JPEG; you can view the < 1 MB PDF here):

Warning: Clicking on this image will load a 6 MB JPEG.  Click here for the < 1 MB PDF.

You can also view my page on the Mathematics Genealogy Project.

Some of my academic ancestors of note (just the historically significant names I am familiar with):

• Nicolas Copernicus - known for heliocentrism (a system where the Sun is the center of the solar system) which was in opposition the accepted geocentrism (a system where the Earth is stationary and the center of the Universe).
• Christiaan Huygens - known as the first theoretical physicist, Huygens is also known for explaining Saturn's rings, wave theory and centrifugal force, among other things.
• Jacob Bernoulli - known for discovering the mathematical constant e (2.71828...) among other mathematical contributions.
• Johann Bernoulli - known for his development of infinitesimal calculus and other mathematical contributions
• Leonhard Euler - mathematician and physicist who made contributions to many sub-fields including mathematical notation (e.g. using the Greek capital sigma as notation for summation), graphing and astronomy.
• Joseph-Louis Lagrange - known for development of the calculus of variations and Lagrangian mechanics among other things.
• Jean Baptiste Joseph Fourier - known for the series approximation for discontinuous functions and related transformation that are both named after him, he also was the first to discover the greenhouse effect.
• Siméon Denis Poisson - known for the Poisson distribution which described the probability of a regular event that has no memory (dependency) on the events that happened before the present, among many other contributions to mathematics and physics.
• Johann Peter Gustav Lejeune Dirichlet - mathematician credited with the modern formal definition of a function.
• Jean-Baptiste le Rond d'Alembert - known for his contributions to fluid mechanics and testing for the convergence of a series, among other things.
• Pierre-Simon Laplace - known for work in celestial mechanics (especially work concerning the stability of the orbits in the solar system), the dependence of the speed of sound on temperature, and was also the first to expound upon an object similar to a black hole, among many other things.

So, what does this illustrious heritage say about me?  NOTHING!  Even if you are mentored by the best, it is ultimately up to you to establish and prove yourself.  However, it is humbling to have any connection not only to history but to the science that I've been using for many years.

If you are interested in learning more about academic genealogies and why they are documented in the article "A Trace of Greatness" from the Times Higher Education (6 May 2010).

My Erdös Number

Many people have heard of the "6 Degrees of Kevin Bacon" game, introduced in 1994, where you try to connect a famous person to the actor Kevin Bacon within 6 connections, e.g. X acted in a movie with Y who acted in a move with Kevin Bacon gives a Bacon Number of 2 for actor X and 1 for actor Y.  The idea of six degrees of separation originated in the early 20th century (of course, not with Kevin Bacon) when Frigyes Karinthy conjectured that any 2 people could be connected through at most 5 people.  This was the basis of the Small World Experiment in 1967 by social psychologist Stanley Milgram.

Long before the Bacon Number in the entertainment industry was the Erdös Number (you can also view the Erdös Number Project page) in mathematics.  Paul Erdös was a prolific mathematician authoring the most academic papers in history, many of those in collaboration with others (at least 1,525).  It became a anecdotal measure of prominence in the field to have a low Erdös Number.  So much so, that the American Mathematical Society has a tool to calculate your Erdös Number based on their database of mathematical papers (click here to go to the tool and select the "Use Erdös" button, try "Einstein, A" and you should see his Erdös Number is 2).  Studies seem to show that, if a person has a finite Erdös Number (meaning, have you published a paper with another author that you can use to start your connection), that number is at most 15 with a median number of 5.  It turns out that my number is 5:

1: Paul Erdős & Mark Kac
    Erdös, P.; Kac, M. "The Gaussian law of errors in the theory of additive number theoretic functions",  Amer. J. Math.  62,  (1940). 738–742.
2: Mark Kac & Subrahmanyan Chandrasekhar
    Chandrasekhar, S., Kac, M., Smoluchowski, R., "Marian Smoluchowski: his life and scientific work. Chronological table and bibliography compiled by Alojzy Burnicki. Edited and with a preface by Roman Stanisław Ingarden", PWN---Polish Scientific Publishers, Warsaw, 2000. 141 pp. ISBN: 83-01-00671-4.
3: Subrahmanyan Chandrasekhar & James B. Hartle
    Chandrasekhar, S., Hartle, J. B., "On crossing the Cauchy horizon of a Reissner-Nordström black-hole",  Proc. Roy. Soc. London Ser. A  384  (1982), no. 1787, 301–315.
4: James B. Hartle & Kip S. Thorne
    Thorne, Kip S., Hartle, James B., "Laws of motion and precession for black holes and other bodies",  Phys. Rev. D (3) 31 (1985), no. 8, 1815–1837.
5: Kip S. Thorne & Amber L. Stuver
    B. Abbott, et al., "Detector description and performance for the first coincidence observations between LIGO and GEO," Nucl. Instrum. Methods A 517 (2004), 154 – 179. 

Special thanks to Nathan Urban for finding this low Erdös Number for me (using the tool listed above) - the best I was able to come up with was 8 with a manual search.

NOTE:  I have a revised Erdös Number of 4 - see my next blog post.

Do you have an Erdös Number?  Post it and your connections as a comment below!



Random picture for today's blog: an honest to goodness black widow spider I found dead behind the LIGO Science Education Center today (in Louisiana):

Gravitational-Wave Physics and Astronomy Workshop

Sorry for the lack of posts!  I've been trying to get work done and prepare for the Gravitational-Wave Physics and Astronomy Workshop that I have just returned from.  It was great getting to see Milwaukee (I was just sure to keep my mouth shut about being from Pittsburgh!).  This is the first meeting of a new series that brings astronomers who are interested in gravitational waves together with physicists that are interested in the astronomy that can be extracted from them (gravitational waves, that is).  When I give tours at LIGO, I often remark that there is very little difference between an astronomer and a physicist here since the goal of the research is to observe the universe in a new way.  And that statement is by-and-large true.  But the real difference between us is the detail of knowledge we know about particular things.  Meetings like this are truly working on bridging that gap.

The day before the workshop began, there was a welcome reception at the Polaris restaurant at the top of the Hyatt Regency hotel (where most everyone attending the meeting stayed).  I was thinking about blowing it off since I had been traveling all day, but was VERY glad I went since the restaurant was one of those slowly revolving ones that gave you a great view of the city.  I'd never been to one before so it was a nice surprise.  On top of that, there was wine, beer, Hors d'œuvres and good conversations with colleagues.

The next day started early with setting up the poster presentations (at larger meetings, scientific research posters are presented in place of talks - I plan a whole blog post about these posters soon!).  The poster I brought was about the human vetting of candidate gravitational wave detections for optical follow-up (I wrote about this in a previous blog post).  I was told where my poster would be displayed and when I would be giving my 1-minute "lightning talk" to advertise it.  Below is my poster on display:

The day was then filled with presentations on various topics of interest.  The major points were neutron stars, black holes, super nova, observational techniques, transient astronomy (that is where my poster on following-up on possible gravitational wave detections fit in) and tests of General Relativity.  About 160 scientists attended this meeting.  Below is a picture of about 75% of the meeting room showing a presentation in progress:

Want to know the real secret about meetings like this?...  The real progress happens during coffee breaks and meals.  This is the time that people can talk one-on-one and collaborate.  For example, at the welcome reception (that I was thinking about blowing off), I ran into a friend of mine who is working on a book about gravitational wave astronomy.  Through talking with him, I expressed interest in the book and now I will likely be giving it a proof/comment read.  Then, at the banquet (more on that below), I ran into another colleague who is working on expanding LIGO's outreach to schools by working on a program that will bring scientists into classrooms via internet conferencing (like Skype).  Since this is something I've been wanting to do for a while now, I am now working with them on this project.  (If you are a teacher, and would be interested in having me Skype with your classroom, please contact me at amber@livingligo.org.  There is also a program called "Skype in the Classroom" where you can sign up to participate collaboratively with other teachers.)

One of the things to really look forward to during the meeting is usually the conference banquet.  This time, it was at Discovery World (a science museum).  We were treated to a reception in the aquarium part of the facility followed by a very nice dinner.  There is nothing neater than to have a good drink while getting to explore a museum (and touch sting rays).  I took the picture below during dinner.  It isn't the best picture and only shows a few people, but I took it and now you get to look at it :)

When the meeting wrapped up after 3.5 very full days, I was excited by the experience but tired and ready to go home.  One of the best parts of the little down time I did have was the view from my hotel room.  I was on the 11th floor of the Hyatt Regency and had a great view of downtown Milwaukee:

On a side note: this hotel was the location where then presidential candidate Theodore Roosevelt was shot while campaigning in 1912.  (The hotel was then the Gilpatrick Hotel.)  He then went on to deliver his campaign speech and mentioned more than a few times that he had been shot and that "it takes more than one bullet to kill a Bull Moose."  The bullet entered his chest bust didn't damage his lungs since the bullet first passed through a steel eyeglass case and a 50 page draft of his speech.  Since the bullet didn't pose a threat to his health, it was determined to be more dangerous to remove it than to leave it alone - he carried that bullet in his body for the rest of his life. (You can read more about it here.)

Louisiana Science Teachers' Association Meeting & X-Rays

I've been away on travel to the Louisiana Science Teachers' Association (LSTA) Meeting last week in Monroe, LA.  LIGO goes to present workshops and to advertise the Science Education Center (SEC) though a booth in the exhibit hall. 

Our booth in the exhibit hall featured a projection of the LIGO documentary "Einstein's Messengers", the Visible Vibrations exhibit from our exhibit hall, 'snacks' (inexpensive, miniature versions of exhibits that teachers can build and use in their classrooms - the Exploratorium has a nice catalog of 'snacks' here), brochures, and posters.  While it was tiring being on your feet all day interacting with the teachers, it was also extremely rewarding!  One of the most inspiring people I interacted with wasn't even a teacher.  One of the security staff was so fascinated by the Visible Vibrations exhibit, that he kept coming back and interacting with it for most of the day!  To see someone who isn't even our target audience (at least that day) exploring the physics involved was extraordinary.  On top of that, he made some of the most spectacular vibration patterns I've ever seen!

LIGO also presented two one-hour workshops.  The SEC director presented one on motors and I presented another one on the LaserFest kits that I based the LaserFest Teachers' Day on a few weeks ago (you can read more about it here).  I had enough kits for 30 attendees, but my workshop was at the end of the day on Friday and only had about 10 teachers attend.  While I was a little disappointed (my ego had me convinced that EVERYONE would want to come to MY workshop), it was also a blessing in two ways.  The first way is that I got to have a lot more one-on-one time with the teachers and they had much more time to ask deeper questions than they would have normally.  The second way is that there were extra kits to be had.  The teachers seemed quite happy when I told them they got to keep their kits and, when I asked if they would like to take another kit with them to share with other teachers at their school, their faces lit up.  Each and every one of those kits has now found a good home in a Louisiana classroom.

Today in History...

Today is the 115th anniversary of the X-ray (if you hadn't noticed from Google's Doodle for today)!  I can't count how many of these I've had in my life and how many times they have saved me from some medical trouble, everything from dental cavities to finding my kidney stone.

Speaking of which, the X-ray below is after I had a ureteral stent placed between my kidney and my bladder to bypass my kidney stone and allow my kidney to drain.  The stent is clearly visible and the kidney stone is the little shrapnel looking thing about a third of the way down the stent.  The top curl is in my kidney and the bottom is in my bladder.  I am so happy that both the stone and the stent are gone!

Initial LIGO is Dead! Long Live Advanced LIGO!

Today (20 October 2010), at 8:00 am CDT (13:00 UTC) the sixth science run of the Initial LIGO detector concluded and, with it, the life of Initial LIGO.

At 11 am CDT time, the announcement was made at the Livingston Observatory that the detector was laser safe (meaning that the lasers are off and no eye protection is needed to approach the instrument).

The 4 km arms (which have not been exposed to the atmosphere for about a decade) have been sealed to preserve their vacuum and the chambers holding the optical instrumentation are being vented (allowing the atmosphere back into the individual chambers).

Work has now officially commenced on the Advanced LIGO installation (whose design and assembly has been going on for years now).

Advanced LIGO is expected to be online around 2014.

Of course, there will be much more detailed information coming to you on this blog in the future.  I just wanted to share this moment in history with you.  I have been privileged to work on LIGO since before our first science data was taken on August 23, 2002 (which is not nearly as long as the pioneers of LIGO have been laying the foundation) and feel even more privileged to be a small part of its history today.  I can't wait for what's to come.

Long live Advanced LIGO!

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, www.atlasoftheuniverse.com.)

Multi-Messenger Astronomy

Right now, I am getting to participate in the growing field of multi-messenger astronomy.  Yes, right now!  "How can you possibly write a blog post while doing this exciting science?", you ask...  Well, because there is a lot of waiting involved.  But before I get into exactly what I am doing right this second, let me tell you a little bit more about multi-messenger astronomy...

Humans have been doing astronomy from the dawn of time by simply looking into the night sky and observing the stars and the Moon and the Sun.  But the largest advances in astronomy have come when we've devised new ways of observing our Universe.  Galileo used a telescope for the first time to discover moons around Jupiter, phases of Venus, and Sun spots.  All of these observations add up to prove Copernicus' theory that the Earth is not the center of the Universe (and this proof ended up landing Galileo under house arrest for the rest of his life).  In more modern times, we've observed the Universe with different forms of light: we've discovered pulsars when we observed the Universe with radio waves, we discovered the Cosmic Microwave Background (CMB) the first time we turned on a microwave telescope (which won the 1978 Nobel Prize in Physics for evidence supporting the Big Bang) and we discovered extraordinarily energetic gamma-ray bursts from deep space (by accident when satellites orbiting Earth were looking for gamma rays from atomic bomb detonations) whose origin we still don't fully understand.  The moral here is that every time we looked at the Universe in a new way, we discovered something we didn't expect to that revolutionized our understanding of the Universe.

Today, we can do astronomy with means other than light.  For example, neutrinos.  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 billions of neutrinos from the Sun passing through your body every second?!).  Neutrinos are also emitted when a star dies in an explosion called a supernova.  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.

LIGO has been participating in multi-messenger astronomy for years by looking for gravitational wave counterparts from observed gamma-ray bursts (observing gravitational waves from a gamma-ray burst would tell us much about their mysterious origin).  Now, we are also participating by analyzing our gravitational wave data in real time to notify several partner telescopes when we think we may have detected something.  If we could observe an optical counterpart to a gravitational wave detection, not only would that be a gold plating on a first detection but we would be able to combine the information learned from both means of observation to have a deeper understanding of what we just detected.

So, what I am doing right now is waiting for a candidate gravitational wave to come through LIGO's data analysis pipeline so that I can look at how the detectors were working and make the decision on whether to send this event out for optical observation (those of us who specialize in this take 8 hour shifts for continuous 24/7 coverage).  Since LIGO has not made a direct detection of gravitational waves yet (and we didn't expect to - more on that in another post) we expect everything we send out to be a false alarm and our telescope partners know that.  But the potential of an event being real... well, that's why I do what I do; I want to be on the front lines when gravitational wave astronomy revolutionizes the way we understand our Universe!

P.S.  The is the view outside my office window right now.  The building to the left contains the input, output and corner optics of LIGO (LIGO is an 'L' shaped detector).  The concrete tunnel that goes off to the right and out of the frame is one of the arms of LIGO (the other arm comes out of the back of the corner building from this view and through the area of no trees in the back - you can see it if you look close).  Each of the arms are 4 km long (in our everyday units in the United States, that is about almost 2.5 miles).  The white silo in the middle of the view is filled with liquid nitrogen (at a temperature of −321 °F) that we use to help maintain the vacuum inside of LIGO (there is over 300,000 cubic feet of vacuum at one trillionth the atmospheric pressure inside of LIGO).