Q: What Do Gravitational Waves "Sound" Like?

Okay, this isn't a question that I usually get asked but the answer to this question is the basis of my answer to questions about how we can determine information about what produced a gravitational wave from the signals we detect.  So, how do we do that?

One convenient feature of LIGO is that it is most sensitive in the frequencies that the human ear could hear if gravitational waves made sound - but they don't.  I can't stress this enough: gravitational waves do NOT make sounds since a sound waves are fundamentally different from gravitational waves.  But, if we take the data we gather from LIGO of a gravitational wave, we can put that signal through speakers and convert them into sound.  In this way, LIGO is very much like a gravitational-wave radio...


LIGO AS A GRAVITATIONAL-WAVE RADIO

Radio stations broadcast radio waves at a specific frequency (this is the number that you tune your radio to) and music is encoded onto this wave.  Whereever you are right now, you are most likely surrounded by radio waves from numerous stations but you can't hear radio waves or the music that is encoded onto them.  To hear this music, you need to have an instrument that can detect the radio waves, decode the music from them, and turn this signal into sound using a speaker.  Now, you can hear the music.

LIGO is a completely passive detector (meaning we just wait for something to happen, we cause nothing that we can detect other than noise) just like your radio is passive (it can't create music).  We wait for a gravitational wave to pass by Earth, and if it is strong enough and in the frequency range that we are sensitive to, then LIGO will detect a signal.  From that signal, we can extract information about what made the gravitational wave, like a radio decodes the music from the broadcast radio waves.  Once we have detected the signal, we can put that signal through speakers to convert it into sound.  Just like a radio, it is the speakers that make the sound and not the detector.  Since LIGO is sensitive to frequencies that are in the same ranges of sounds we can hear, we can hear the gravitational-wave signals when put through a speaker.  Now we can extract information about what made the gravitational wave just like we can hear the different instruments and voices in music.


LIGO'S SENSITIVE FREQUENCIES = AUDIBLE FREQUENCIES

Initial LIGO's most sensitive range (as we were before we started our current upgrades) was between about 60 Hz to 800 Hz.  This corresponds to the lowest note on a cello (click here to hear what 65.41 Hz sounds like) to the lower notes on a piccolo (click here to hear what 523.25 Hz sounds like), respectively (according to Wikipedia).  Once Advanced LIGO is complete and operating at sensitivity, it will be more than 10x as sensitive as Initial LIGO and its most sensitive region will be between about 20 Hz to 2000 Hz (this is the range that produces at least 10x the sensitivity of the sensitive range noted for Initial LIGO).  This corresponds to the lowest frequencies humans can hear (like the lowest note on a tuba) which is usually felt more than heard to a little below the highest note on a flute (click hear to hear what 2093 Hz sounds like).  LIGO's sensitivity to different frequencies are shown graphically below:

LIGO sensitivity vs. frequency (see this post for a description of how to interpret this plot).
Click on the graph to see a larger image.

Recall from a previous post that it is because LIGO is most sensitive to the audible frequency range that we cannot detect gravitational waves from the Moon, Sun, and planets; they produce gravitational waves at much lower frequencies.


THE "SOUNDS" OF DIFFERENT KINDS OF GRAVITATIONAL WAVES

We can tell just from what a gravitational wave "sounds" like what category it is classified as; there are 4 major categories:

1. Inspiral gravitational waves: two massive objects orbiting each other faster and faster as they get closer together and eventually merge into one.  Pairs of neutron stars, black holes, or the combination of the two are prime candidates for detection.
     ⇒These waves are expected to sound like a "chirp" (click here to hear the example in the plot below):





2. Continuous gravitational waves: a distorted object rotating about its axis with a constant frequency (the Earth rotates with a very constant frequency of once per day).  A neutron star rotating rapidly with a "mountain" on it are prime candidates.  ("Mountain" is in quotation marks because it is a deformation as little as a few inches high on the nearly perfectly spherical neutron star.)
     ⇒These waves are expected to sound like a single tone (click here to hear the example in the plot below):





3. Stochastic gravitational waves: many weak signals from different sources combining into one "jumble" of a signal.  Relic gravitational waves from the Big Bang are expected to be candidates for detection.
      ⇒These waves are expected to sound like static noise (click here to hear the example in the plot below):





4. Burst gravitational waves: these waves are short duration and from unanticipated sources or from known sources where we can't be sure what the gravitational waves will "sound" like.  I like to call these the gravitational waves that go 'bump' in the night.
      ⇒These waves are expected to sound like 'snaps', 'crackles', and 'pops' (click here to hear the example in the plot below):

While is is great to see and hear the differences between the different kinds of gravitational waves, it is harder to see how we can glean more specific information about the thing(s) that made the gravitational wave.  The answer is that we can use general relativity to predict what kinds of signals ("sounds") a certain situation will create.  Below is a movie by Steve Drasco (Caltech/CalPoly) showing the sped up evolution of a body 270 times the mass of our Sun orbiting and finally merging with a supermassive black hole 3 million times the mass of our Sun.  The movie starts one year before the two objects merge and the bottom of the frame shows a graph of the gravitational waves while the majority of the frame shows the orbit of the system.  As you listen, you can hear how the tone changes into the chirp that is characteristic of this kind of system (the movie is ~13 MB so it may take a minute or two to load):

 

By studying the predictions of what different gravitational waves will "sound" like, we can translate a detected gravitational wave into information on the system that made it.


DO WE ACTUALLY LISTEN FOR GRAVITATIONAL WAVES?

Yes and no...  The option to listen to the data as it is collected is available to scientists working in the LIGO control room.  I've done it but I don't make a habit out of it since almost all of what LIGO detects is small vibrations from our environment.  You can listen to real LIGO noise by clicking here (if you carefully listen all the way to the end, you can hear a fake inspiral chirp that has been added to the data - you may miss it).  Since what you predominantly hear sounds like static, it can lull you to sleep which isn't advisable when you are the responsible scientist on duty!  Also, almost all gravitational waves will be too weak to hear with our ears which is why we mainly analyze data using sophisticated data analysis techniques that have been specially designed to search for each of the four categories of gravitational waves.  (This is what I do for a living!)

I also wrote in March 2011 about a fake signal that was placed (injected) into the LIGO data to test if our data analysis techniques could really detect a gravitational wave if there was one.  This was a blind test (called the "Big Dog" due to its apparent location in the constellation Canis Major) meaning that only a few individuals knew about this fake signal and the rest of us were left to find it and interpret its results.  While we did not detect this signal by listening to it, it can be heard in both the LIGO detectors (about 17 seconds into the recording linked below).  This is real LIGO data and the sound may be VERY LOUD - so turn your volume down before you play it and then adjust it!
     ⇒Click here to hear the data around the blind injection for LIGO Hanford, WA.
     ⇒Click here to hear the data around the blind injection for LIGO Livingston, LA.*
          *Note that there is a audible instrumental "glitch" in the Livingston data about 8 seconds into the recording; this is unrelated to the injection.

While it is difficult to hear gravitational waves that will be buried in detector noise, there is no denying that the human brain is very effective at breaking sounds down into their individual components.  A recent Physics Today article titled "Shhhh.  Listen to the Data" discusses the advantages of humans listening to data and features a discussion of this application to LIGO.  Also, if you want to test your ear's talent at "hearing" gravitational waves, there is a fantastic website called Black Hole Hunter which places black hole gravitational wave "sounds" (like the system in the movie above) into simulated data and tests if you can discern the signal.  I've spent many an hour playing with this and even use some of the cell phone ringtones they've made (also available on the Black Hole Hunter site).

*** If you are interested in more gravity games, see my Gravity Games page (link here and under the blog banner)! ***


WANT TO HEAR MORE?

There are some great sites that feature the "sounds" of gravitational waves.  Here are a few of my favorites:

• Black Hole Hunter
• Scott Hughes' (MIT) page of gravitational wave sounds (and a more out of date one)
• black-holes.org page of gravitational wave sounds

Q: What Would a Gravitational Wave Feel Like?

Several people who have found this blog were led here after searching for this question:

What would a gravitational wave feel like?

This is an excellent question so I decided to answer it directly in today's post...


HOW DOES A GRAVITATIONAL WAVE INTERACT WITH MATTER?

First, let us review what a gravitational wave does to matter as it passes by.  Gravitational waves will expand space in one direction and compress it in the perpendicular direction.  This stretching and squishing happen in the plane that forms the cross-section of the wave; this is perpendicular to the direction the wave is traveling.  For a gravitational wave traveling into your computer screen, a circle of stuff will be affected like this:

Image from Wikipedia [gravitational waves]

HOW WOULD A GRAVITATIONAL WAVE FEEL FOR A SOURCE FAR AWAY?

Now let us consider what you are likely to feel here on Earth from what we here at LIGO consider to be "big" gravitational waves.  These waves are produced by some of the most violent, energetic things in the Universe like black holes colliding and stars exploding.  These sources are rare and there are none nearby us, say within a few light-years.  Since the strength of a gravitational wave decreases as the distance from its source increases, by the time these reach us here at Earth they are incredibly small.  A once every ten years gravitational wave will squish and stretch LIGO less than 1000x smaller than the diameter of a proton (< 1x10^-18m).

Therefore, a person will not feel anything from even the strongest gravitational waves we expect to detect with LIGO.  


HOW WOULD A GRAVITATIONAL WAVE FEEL FROM A STRONG, NEARBY SOURCE?

If we were near one of the huge, violent sources LIGO is sensitive to, the gravitational waves would be strong enough to rip us to pieces!  (So it is a very good thing that these sources are very far away!)  This is due to a phenomenon known as "spaghettification".  In a previous post, I described a gravitational wave as simply a change in the gravitational field moving out into the Universe like a ripple in a pond.  The gravitational field is a measure of how much a mass would feel at any given place.  So, if the gravitational wave is a changing gravitational field, then the force of gravity that a mass would feel as the gravitational wave passes should change too.  If the change is so large (due to a very large gravitational wave), then it is possible that your feet will feel a strong enough force, compared to your head, to rip your legs off your body!  And to make matters worse, the sides of your body would be compressed at the same time.

Below is a clip of Neil deGrasse Tyson giving a humorous description of spaghettification.  His description focuses on what would happen to you if you fell into a black hole, but the concept is the same for super-strong gravitational waves:

CONCLUSION

Given where the Earth is in the Universe and how far away sources of strong gravitational waves are, any passing gravitational waves will be so small that we will never be able to feel them.  But if we were close to a strong source of gravitational waves, they could tear us apart!

So it is both a blessing and a curse that the strong sources of gravitational waves are far away:  a blessing because we will never be harmed by them and a curse because they are so small, that we need huge, extraordinarily sensitive detectors like LIGO to detect them.

The Null Result: NOT Finding What You Were Looking For

I've written many times on this blog about why we are looking for gravitational waves and what we hope to learn from them.  I also get to tell real people about this all the time with the work I do at the observatory.  As they get excited, they want to know how many gravitational waves we've detected.  My standard response (as of this date, of course) is, "None, and we didn't expect to either."  And I say this with a smile on my face.  Cue the confused and disappointed expressions...

With Initial LIGO, we were hoping to maybe see a gravitational wave from a pair of dense stars merging together about every ten years or so (based on astronomers' estimates on how many of these system there are out there and what fraction of them will be in this merger stage).  While LIGO has been taking data on and off (we take breaks to improve the detector) since 2002, we only have about 2 years of data when both LIGO detectors (in Louisiana and Washington state) were collecting data at the same time (things like earthquakes, weather, etc. can put one or both offline temporarily).  This gives us about a 20% chance of detecting a gravitational wave with LIGO - not the best odds but better than humans have ever done before!  When the Advanced LIGO upgrades are done and the detectors are running at their design sensitivity, we expect to find one of these "merger" gravitational waves about once a month!

An artist's impression of two stars orbiting each other and progressing (from left to right) to merger with resulting gravitational waves. [Image: NASA]

So, what have we been doing with all this data that has no gravitational waves in it?  Some may think it is worthless but that is far from the truth!  Most people think that when you do an experiment and don't find the thing you are looking for (a null result), the experiment was a failure.  While that can be true if your experiment is inherently flawed, it can also tell you valuable information about the world and Universe around you; now you know how something doesn't work or how rare something is.

Since we know that gravitational waves exist from the observations of the Taylor-Hulse pulsar (1993 Nobel Prize in Physics), we know gravitational waves are real.  So we are left with knowledge on how rare gravitational waves are.  We estimate this by carefully studying how sensitive our detectors are and how well our data analysis methods perform.  Once you know these things, you can combine that with how long you looked for gravitational waves (how much data was taken) and estimate the highest rates that the different kinds of detectable gravitational waves pass by Earth.


THE UPPER-LIMIT FOR BURST GRAVITATIONAL WAVES

I am going to use the example of burst gravitational waves which are short duration gravitational waves from unanticipated sources or from known sources where we can't be sure what the gravitational waves will look like, e.g. supernovae, etc.  (The science summary for this work is here.)  I chose this example because this is the kind of gravitational waves I specialize in.

In order to determine the sensitivity of our data analysis method, we need to put fake signals into real data and measure how many of each kind and strength are found by our data analysis method.  This gives us our efficiency.  When combined with the amount of data collected (giving us a measure of how long we were sensitive to gravitational waves) we can estimate the maximum rate that we would expect a kind of gravitational wave to pass by Earth.  We used many different signals to test the data analysis method, but my favorite is called a sine-Gaussian and looks like this:

Sine-Gaussian signal: a sine-wave (trigonometry) multiplied by a bell-curve (Gaussian function).  The horizontal axis measures time in seconds and the vertical axis measures the strength of the signal.  The spacing between the waves provides a measure of frequency.

Using different strengths and frequencies of this signal, we were able to set an upper-limit on the rate of these kinds of gravitational-wave bursts:

Upper limits on the rate of gravitational wave bursts, determined using the LIGO and Virgo data. The different curves represent signals with different characteristic frequencies; the vertical position of each curve shows what rate should have given us at least one detectable burst with 90% probability, for different assumptions about the strength of the burst (horizontal axis). Since no signal was detected, higher rates are ruled out with good confidence.  [Source: S6 Burst Science Summary]

The current results for the burst upper-limits (from the plot above) are that we expect up to about 1.3 sine-Gaussian-like signals a year in LIGO's most sensitive frequency range (64-1600 Hz) with 90% confidence.  


RESTRICTING PARAMETERS ON OBSERVATIONS

Another thing you can do with data that doesn't contain gravitational waves is restrict the possibilities on how observed events happened.  In 2007, there was a strong gamma-ray burst (GRB) observed by the InterPlanetary Network (IPN).  The area that the source could have originated from also overlapped with an arm of the Andromeda Galaxy:

Bottom left corner box: possible area where GRB 070201 could have originated.  Remaining part of image: close-up of the part of the candidate source area that overlaps the Andromeda Galaxy.  An dwarf spheroidal galaxy, called M110, is also labeled.

This was very exciting to all of us at LIGO because one of the possible causes of gamma-ray bursts is the merger of two neutron stars (like in the first image in this post).  With the Andromeda Galaxy being only about 2.5 million light-years away (LIGO was sensitive to these merger gravitational waves all the way out to several hundred million light-years away), if it really was a merger that caused this GRB then we should have seen it!

After careful analysis of our data before, during, and after this GRB, we did not find any evidence of a gravitational wave.  While it would have been very exciting to see something, this null result tells us that:

1. if the GRB was located in the Andromeda Galaxy, it was not caused by a neutron star pair merger, or
2. if the GRB was created by a neutron star pair merger, it was located far behind the Andromeda Galaxy. 

A LOT FROM SEEMINGLY NOTHING...

As of today (14 June 2012), LIGO has submitted 64 papers for publication.  You can also read the public science summaries for the latest published papers here.  This a quite a lot of papers based on data without any gravitational waves!

Q: How Can Gravitational Waves Help Mankind, Part II: Spin-Off Technology

Previously, I have blogged about how gravitational waves can help mankind.  In that post, I noted that observing gravitational waves will allow us to perform unprecedented astronomy, investigate physics in extreme situations that cannot be replicated on Earth, and allow us to further test general relativity.  I also noted that there have been huge advances in technology developed by LIGO scientists and engineers just to make LIGO work.  LIGO has started to document these spin-off technologies on a new webpage: LIGO Technology Development and Migration.

The page describes many methods of how new technology and techniques move from the LIGO research environment to industry or other research applications.  These modes include patents to serendipity (among many others).  I found the descriptions here interesting myself; as a scientist in the thick of it, I am not always aware of how the things I and my colleagues are developing are affecting the world outside of my own little universe.  Also documented on the LIGO Technology Development and Migration page are descriptions of some of the spin-off technology LIGO has produced.

I want to take this opportunity to tell you about just few of the spin-offs that I am most familiar with: 

HOW DO YOU HANG MASSIVE OBJECT FROM A THIN GLASS WIRE?

One of the new additions to Advanced LIGO will be that the mirrors used to measure gravitational waves will be suspended like pendula from glass wires (the pendulum suspension isn't new, it is the glass wire that is new).  It turns out that the metal wires we use like to vibrate right around our most sensitive region in LIGO (about 320 Hz).  This frequency is due to the fact the the wires are made of metal.  If we use wires made from the same material as our mirror is made of (fused silica) then the frequency that they like to vibrate at is outside of our "sweet spot" region (between 100-1000 Hz).  But, our new mirror will be about 40 kg (~88 lb).  It may be surprising, but the glass wires are strong enough to support this weight (which is also the weight of a small child).

Silica fibers bonded to "ears" that are attached to a glass mass

But how do you connect these delicate glass wires (they may be strong, but they are brittle)?  That is the work of Sheila Rowan, James Hough, and Eoin John Eliffe from the University of Glasgow and Stanford University.  They has developed and patented a new technology that not only bonds the wire to the mass, but also minimized contamination of the collected gravitational wave data from glass' thermal noise.  This technology has already been transferred to several optical industry vendors!

Read more about this here!

HOW CAN YOU KEEP THE SHAPE OF A LENS FROM CHANGING WHEN A LASER PASSES THROUGH IT?

In LIGO, it is very important to keep the shape of our mirrors controlled so that we can keep the laser light bounding back and forth in an arm many times before it recombines with the light from the other arms (this makes the light think that our arms are 70-100 times larger than they are and that gives a gravitational wave more time to affect the light in the arm).  Even though our mirrors are nearly perfectly reflecting, a small amount of the light gets absorbed by the mirror and this causes it to heat up.  When the mirror heats up, it warps its shape and this distortion can make it VERY difficult to keep the light focused between two mirrors that are 4 km (~2.5 mi) apart.  What to do?

The solution to this is the heat the mirror in a controlled way so that you can cause your own distortions that compensate for the warping that the laser is causing.  LIGO has spent much effort perfecting techniques light this (I even have a friend who did his Ph.D. research on this).  This also has wider application in industrial and military environments since higher power lasers are being introduced all the time (such applications include welding and material cutting).  The ability to control the shape of the optics that control and direct a laser beam is becoming increasingly important.

Read more about this here!


HOW CAN YOU USE LIGO DATA ANALYSIS METHODS TO ANALYZE OTHER KINDS OF DATA?


This one is dear to my heart since I specialize in LIGO data analysis!  It is not just physical technology that can be reapplied for other purposes; techniques and software can as well.  Of the many different analysis methods that LIGO executes, the one used to search for continuous (long duration with consistent frequency) gravitational waves produced by things light neutron stars with a "mountain" on it (I put "mountain" in quotation marks because a neutron star is so perfectly spherical, that a deformation of less than an inch is considered a "mountain"!).  This is the analysis that is performed by Einstein@Home (which I blogged about previously here).  

Arecibo Radio Telescope (image from Wikipedia)

The data analysis challenge for these gravitational waves turns out to be similar to the challenge faced by astronomers looking for pulsars that emit either radio waves or gamma rays.  This data is collected by the Arecibo radio telescope in Puerto Rico and the Fermi gamma-ray satellite, respectively.  Using Einstein@Home, the continuous gravitational wave data analysis techniques are applied to data from these two detectors to great effect!  The number of known gamma ray pulsars (that don't produce radio waves) has been increased by a third thanks to discoveries made using the same data analysis Einstein@Home uses.  Radio pulsars are also being discovered on a regular basis with Einstein@Home; since the beginning of 2012, 22 new radio pulsars have been discovered!

Read more about this here!

The Two-Body Problem: Relationships and Physicists

THE PROBLEM OF DUAL CAREER RELATIONSHIPS IN ACADEMIA

One of the more difficult things about being a physicist in a relationship is that your partner is usually also a professional in a technical field as well.  Working in specialized fields make finding jobs in the same location as your partner difficult.  So many of us have experienced these issues that we have a special name assigned to it - the two-body problem (re-purposing the phrase referring  to the physics of two masses interacting, say in orbit).

The problem isn't about finding work, but finding work working in our specialties.  For example, I am a skilled physics educator and every college and university teaches physics at some level so there are job opportunities for me in that respect.  Of course, these jobs are still very competitive to earn, but you get the idea that there is work out there.  But many of these jobs would likely be strictly or mostly teaching without much in the way of research opportunities.  I could be employed but I would likely not be able to continue my LIGO research which is important to me.  There are about 80 institutions from across the country and around the world that work in the LIGO Scientific Collaboration (click here for a list of these institutions).  While this sounds like many, the odds of not only landing a job at one of these institutions and having fulfilling job prospects for a spouse isn't great.

My two-body problem was made official in 2003.

MY TWO-BODY PROBLEM

This is usually most difficult for us academics as we finish our degrees (or when an appointment ends if the relationship started when not a student - mine did so this is what I reference).  For me, it was especially stressful since I finished my doctorate before my husband finished his.  My solution to the two-body problem: take a mini retirement.  He was supposed to graduate next semester so I figured that I would wait for him.  Besides, after writing my dissertation, I was quite burned out on research.  Well, next semester turned into the next next semester and I started to quickly lose my mind as I wasn't nearly as burned out as I thought.  I had a small contract teaching job at Penn State, but it was something that I had been doing for years as a graduate student and it wasn't challenging or time consuming.  Then I discovered vampire books and decided to do a normal person job for fun (almost all of my work previously has been in academia).  One of my students gave me tips on where to apply for a waitressing  job.  I was looking for something in the evening, like in a bar, but I ended up with breakfast/lunch service at a hotel restaurant.  Except for the very early start time (I had to be there for 6 AM, which I know isn't that early, but doesn't exist in my universe), I loved the work!  I met lots of new people and none of them treated me like I was odd because I was a physicist (since they didn't know).  This did come at a potentially steep cost professionally since effectively being out of the field for nearly a year (like I was) is usually career suicide.

Finally, there came a job I was willing to suffer a long distance relationship for - the one I have right now.  It was pure serendipity that they were also hiring engineers with my husband's skills at the same time.  We both got jobs and we are both happily employed at LIGO now.  This is EXTREMELY rare.

Now my concern is maintaining the ability to sleep under the same roof with my husband in the future.  My job here is a postdoctoral scholar is temporary, much like a medical doctor's residency.  I've been at this job for almost 5 years now (I did get promoted to senior postdoctoral scholar after my third year) which is a long time to be a postdoc at the same place.  That's not to say that it's unusual to have several postdoc appointments at different places for more than 5 years.

What to do now?  Well, I am trying to work out a new position but I don't want to jinx by talking about it here now.  This solution would let me stay put but definitely mix things up a bit for me.  Fingers crossed!

THE TWO-BODY PROBLEMS OF MY MENTORS

To give you an idea of how lucky I am to live with my husband through our transition from student to scientist, I've had two advisors on my way to getting my Ph.D. who both had extended long-distance relationships due to the two-body problem.  The first was Gabriela Gonzalez who left Penn State to go with her husband (also at Penn State) to LSU where he was offered a prestigious position and she would be able to work much closer to LIGO.  Before they found the Penn State (and then LSU) solution to their two-body problem, they worked for about 6 years hours apart from each other (you can read about their story here - you may need to register, but it's free).  When I turned down the opportunity to go to LSU with her (due to my own relationship), I then worked for Sam Finn at Penn State.  He and his wife also spent about a decade apart before they found their solution.

Conclusion, I am lucky beyond belief to not only have a job that I love but to have the one I love with me as well.

Read More:

A Dual Dilemma  (NatureJobs.com)
Is the Husband Going to be a Problem?  (New York Times)
Women in Academia: The Two Body Problem  (Persephone Magazine)

News on LISA and Some Personal Stuff

LISA NEWS...

The LISA Symposium was in Paris this week and the result of this meeting was a strengthening of the efforts to put a gravitational-wave detector into space and the formation of the eLISA Consortium.  Below is a statement issued by the Consortium:

Getting ready for next time:

European gravitational wave community strengthens its space collaboration

During the 9th international LISA Symposium, held May 21 – 25 in Paris, the international LISA* community analyzed the new situation after ESA´s decision to choose JUICE for Europe´s next large space science mission. As the eLISA** mission, despite not being selected, was reported to have been unanimously ranked first by ESA´s scientific review committee in terms of scientific interest, strategic value for science and strategic value for the projects in Europe, the community is in good spirits: this is the first time that any space agency committee has ranked a gravitational wave observatory as its highest scientific priority. In order to prepare a strongest possible bid for the next launch opportunity the community has decided to continue its collaboration as the self-funded and independent eLISA consortium.

Besides preparing for the next competition the consortium will strongly support ESA's LISA Pathfinder mission, whose launch in 2014 will finally open the door to approval of a full gravitational wave mission. LPF will demonstrate key gravity-measuring technologies in space for the first time, preparing the way not only for gravitational wave detectors but also for next-generation Earth and planetary gravimetry.

The eLISA consortium consists of a management board, a steering committee, and working groups in science, technology and data analysis. It represents the European states involved in eLISA, i.e. Denmark, France, Germany, Italy, Netherlands, Spain, Switzerland, and UK. The consortium is led by Prof. Dr. Karsten Danzmann, who chaired the former LISA International Science Team and is a director at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) and a professor at the Leibniz Universität in Hannover, Germany.

“Our goal is to keep this highly motivated and effective scientific community together. It has attracted many young and excellent researchers. The knowledge and innovative potential of our community is documented in more than 2000 published scientific papers - we want to keep it working on a strong science, technology and data analysis programme”, says Karsten Danzmann, describing the role of the eLISA consortium.

Colleagues from the US, China and possibly other interested countries will be invited to participate. At the LISA Symposium, US participants presented results on a comparative study of low-cost LISA variants and expressed interest in contributing to an ESA-led mission. And for the first time, a large Chinese delegation participated in the LISA Symposium and announced their scientific interest in a close collaboration on a gravitational wave mission. The Chinese Academy of Sciences and the Chinese Space Agency are developing their own plans for a gravitational wave detector in space.  

LISA*: Laser Interferometer Space Antenna

eLISA**: evolved Laser Interferometer Space Antenna, also known as NGO (New Gravitational-Wave Observatory)

PERSONAL STUFF...

It's been a long while since I posted on here about myself.  One of the reasons I started this blog was that I wanted to humanize scientists and the work they do; you wouldn't believe how often visitors tell me that I'm not what they expected from a scientist (they mean that as a compliment) or that I was more normal than they expected.  I pulled back on writing much about myself simply because I wasn't nearly as interesting as I first thought.  I can be summed up pretty well by: loves vampires, has migraines, and is sometimes insecure about her professional worth.  (This post is even being published a day late because a migraine.)


But there has been some excitement in my life.  Over the last two weeks I have been catching up on all of my routine doctors appointments I have been putting off due to my work schedule and my husband's (and we share a car since we work at the same place).  He was out of town for nearly 2 weeks so I had the car to myself!  I've seen by dermatologist (I am very fair skinned and I get checked out for skin cancer), my gynecologist, my dentist, my cardiologist, and my urologist.  The good news is that everything is going well even though I was up to 6 months behind on being seen.  The bad news is that I've let my depression get the better of me these past few months and I didn't realize what a bad place I was in until I had time to myself.

I've been wondering whether or not to talk about this on my blog since I have had some outright ignorant reactions when I mention that I have depression.  But, May is Mental Health Month and I would like to talk a little about dealing with depression and anxiety and why you should seek treatment if you suffer from this as well.

I was an anxious little kid who was sad a lot.  As I grew up and started to have more adult problems, these tendencies became more pronounced.  It took a traumatic event for a doctor to recommend treatment for depression.  This treatment took some time to work, but when it did I realized that I had basically lived my whole life depressed to some extent and simply thought that was what normal was.  I don't need constant treatment for it, but if I'm not careful depression can sneak up on me so slowly that I don't notice it happening until it becomes horrible.  That is what happened for me recently and even then it took a doctor to bring the point up (I guess I'm not as good at covering it up as I thought I was).  I'm being treated again and things are starting to look brighter.  At least I don't feel alone and isolated even when I am surrounded by friends and colleagues.

My point is, if you think you are depressed or feel anxious for extended periods of time, talk to a doctor, medical or psychological.  I've been told to just "get over it" or called weak because I have sought treatment for my depression.  Well, will power can only help you look like nothing is wrong but you will still be depressed.  And I have discovered that most of the people who call me weak have similar problems of their own that they won't seek help for.  Truly, treating my depression is the best thing that I have ever done and I am not sure if I would be where I am today if I had not.

Q: What is a Gravitational Wave?

Many times, when we scientists answer this question, we say "ripples on space-time".  It wasn't until I was in grad school that I really started to understand was "space-time" was.  Before that, anytime someone said the word I just nodded with an expression of recognition so I wouldn't look dumb.

So, when I talk to visitors to LIGO, I like to talk about gravitational waves (or, more specifically, space-time) in a different way.  First, let's go back to gravity as Newton described it...

NEWTON'S GRAVITY

There is a story about how Isaac Newton came upon the realization of gravity, often referred to as "Newton's Apple".  One day, Newton was sitting under a tree in an apple orchard.  This was one of those days when the Moon is visible in the afternoon sky.  He then saw an apple fall to the ground (some versions of the story say the apple fell on his head but I think that is too convenient).  It was then that he realized that the force that drew the apple to the ground without touching it was the same force that kept the Moon in orbit around the Earth.  This kind of force is called action at a distance.  The way two masses communicate the gravitational force between them is with a field (just like the magnetic or electric field).  Every mass (including you and me) fills up the Universe with a gravitational field that gets weaker with distance.  When objects move, the entire gravitational field of the object moves with it and every object in the Universe feels a change in the gravitational force because of this instantaneously.

EINSTEIN'S GRAVITY

In Einstein's relativity, nothing can travel faster than the speed of light, including information about where mass is in the Universe.  That means that there must be a change in the gravitational field that moves out into the Universe at a finite speed instead of everything "feeling" the change instantly.  A gravitational wave is really that change in the gravitational field propagating out into the Universe like a ripple on a pond.

SPACE-TIME

So, how is this moving change in gravitational field that is a gravitational wave related to space-time?  First, space-time measures the curvature of the Universe.  It is usually visualized as an elastic grid, but this is a large simplification since space-time would be better represented by an animated 3-dimensional grid - but that is beside the point for now.  When there is no mass, space-time is perfectly flat:

When there is mass present, space-time will be curved:

Consider another much smaller mass approaching this one: it will be deflected by the curvature of space-time.  This is gravitational attraction.

Ultimately, the strength of the gravitational field at any given place corresponds the the steepness of the curvature of space-time there.  In the flat space-time, there is no curvature and no gravitational field.

RIPPLES ON SPACE-TIME = RIPPLES OF GRAVITATIONAL FIELD

Now, we can go back to the phrase "ripples in space-time".  Now that we understand more about what space-time is, how it is represented, and how it affects mass moving through it we have a bigger picture of what gravitational waves are.  Any time a mass moves (accelerates - there are some subtleties here), that is going to create a change in the gravitational field (the curvature of space-time) and this change will ripple out into the Universe.

Below is an animation by the Jodrell Bank Center for Astrophysics of a pulsar-neutron star system merging into a black hole.  The green grid represents the surrounding space-time and the gravitational waves on it are evident:

So, what do you think?  Does this make more sense?  Let me know!


ADDENDUM added 15 July 2012:

The elastic 2-dimensional grid, while suitable for discussion here, has several important features that are imperfect for use as an analogy for spacetime.  The first is that an elastic sheet will create a curvature that is related to the object's mass and its size.  However, the size of a mass has nothing to do with the curvature of spacetime.  Another is that a passing gravitational wave will affect a mass but the mass will not continue to 'bounce' on spacetime thus creating more ripples on spacetime (think of a mass bouncing on a trampoline).  There are plenty of other features that make this 2-dimensional approximation imperfect, but these are two of the most important for our purposes.

A better visualization is found in the American Museum of Natural History's short documentary called Gravity: Making Waves (which can be seen in its entirety on my Viewing Fun! page).  This is grid-like scaffolding filling 3-dimensional space in which there is a depression caused by mass.  While it still isn't a perfect representation of spacetime, it is much better than the trampoline approximation above (but also overly complicated for this discussion).  Below is the relevant clip from Gravity: Making Waves (~ 2 MB):