How We Monitor Data Collection with Advanced LIGO

The 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.  But how do we keep the detector working so that we can collect data and how do we know that our data is good?

The LIGO Livingston control room on 3 November 2015 (during O1).

OPERATORS

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!

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. 

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.

SCIENTISTS

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). 

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.

SCIENTISTS: LSC FELLOWS

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.

SCIENTISTS: DQ SHIFTERS

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.

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.

First 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.

Installing one of Advanced LIGO's seismic isolation platforms at the Hanford observatory in 2013.

ENGINEERING RUNS

These test runs are called engineering runs.  We abbreviate them ER followed by the number of the run.  The last one was called ER8.  I've already talked about the first one (ER1) 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.

OBSERVING RUNS

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 the "Big Dog" event) 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.

DETECTION IS POSSIBLE...

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.

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 here.)
aLIGO wil be able to "see" up to 200 Mpc (about 650 million light years).

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.

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.

Advanced 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.

ADVANCED LIGO

On 20 October 2010, Initial LIGO (iLIGO) recorded its last bits of science data [read the blog post here].  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 [you can read all about it here]).  The metaphorical "keys" to the detector were transferred from operations to the aLIGO installation team.

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.

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.)

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 done and working in quote in my parenthetical comment?  Well, now is the time for commissioning.  The detector can turn on and operate as in interferometer 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.

Break time at the Advanced LIGO dedication at the LIGO Hanford Observatory on 19 May 2015.  [Source: LIGO Scientific Collaboration's Facebook page]

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).

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]

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!


IN MEMORY:

Cristina Torres

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 University of Texas at Brownsville 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. 

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 really have figured out, at a regional Conference for Undergraduate Women in Physics (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).

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. 

Until again, Cristina...

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

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!

Q: Why Isn't LIGO Sensitive to GW From the Sun, Moon, or Planets?

Another question I am often asked at LIGO is why we are looking for gravitational waves from the most violent, energetic events in the Universe when the Sun, Moon, and planets are moving around the Earth right beside us.  The reason for this is that there is simply not enough mass (even in our Sun) moving fast enough to produce detectable gravitational waves.  The key here is "fast enough".  Let's look at the sensitivity of LIGO to figure out what is "fast enough"...

Click on this plot for a larger image.

These are the sensitivity curves for all of the LIGO science runs (labeled S1, S2, etc. in chronological order), the design sensitivity for Initial LIGO (iLIGO), and Advanced LIGO (aLIGO).  Remember, like in golf, a lower number is better (more sensitive).  There is a little more to reading this graph:

• The vertical (Y) axis is in units of strain.  That is just the change in length of LIGO's arms divided by their original length (4 km or 4000 m).  The numbers on this axis on in scientific notation (10^-18, etc.).  The negative in front of the super-scripted number (exponent) means the number of places after the decimal place.  For example, 10^-3 is the same as 0.001.  10³ (note there isn't a negative sign here so this is the number of zeros before the decimal place) is 1000.  10^-21 is a strain that corresponds to a change in length of the arms of 1000x smaller than the diameter of a proton.  
• The horizontal (X) axis is frequency which is measured in units of Hertz (Hz, how many crests of a wave pass by every second).  This is also in scientific notation (like mentioned above).  The spacings of the lines are uneven because this is in log (logarithmic) scale.  The line labeled 10² is 100 Hz, the next unlabeled line is 200 Hz, the next unlabeled is 300 Hz, etc.  Each labeled line is 10x more than the labeled line before it.

The frequencies where LIGO is most sensitive is between 100-1000 Hz (10² - 10³ Hz).  At lower frequencies (to the left on the plot) the sensitivity curve takes a sharp turn up to lower sensitivities (remember, a higher plot means lower sensitivity).  This is due to the seismic vibrations that are constantly present on the Earth mostly from the microseism.  The only way to eliminate this noise is to place a gravitational-wave detector in space.

You can see from the sensitivity plot that for our last science run (S6, the yellow-green curve) achieved a sensitivity better than the Initial LIGO design (the black curve just above it).  For Advanced LIGO (the lowest black line) there are several configurations that it can be operated in (more details are here), but the curve represented here produces the best sensitivity over a broad frequency range and is likely to be the general operation state.  Advanced LIGO will have even better sensitivity at lower frequencies, but not enough to be sensitive to objects in our Solar System.

So, what frequency would be the gravitational waves from Sun?  The Earth orbits the Sun once every year (365.25 days or 31,556,926 seconds).  This gives a frequency (f=1/year) of 3.1689x10^-8 Hz or 0.000000031689 Hz.  This is WAAAAY too low of a frequency for LIGO or for any proposed space based detector (like the recently canceled LISA which only goes down to about 10^-4 Hz or 0.0001 Hz):

Plot comparing the sensitivity curves of Initial LIGO and LISA.

Therefore, since nothing with great mass moves in our Universal neighborhood with high frequencies, we must look deeper for things like stars exploding an black holes colliding.  These are much more interesting that just observing the gravitational waves from the Solar System; they really wouldn't tell us much new information about the Universe.  At LIGO we are not just seeking to make the first direct detections of gravitational waves, but we are trying to use these gravitational waves as a new way to do astronomy!

Q: How do we know gravitational waves really exist if we've never directly detected one?

Today's question is one that has been asked of me repeatedly while giving tours of LIGO and talks on the science we do:

How do we know gravitational waves really exist if we've never directly detected one?

One question I often get while discussing LIGO science with others is, "How many gravitational waves has LIGO detected?"  Well, the answer to that is none - yet.  But, we also didn't expect to detect any yet.  During our last science run, we were able to detect gravitational waves that change the length of LIGO's arms about 10,000x smaller than the diameter of a proton.  Even though this is almost an unthinkably small distance, this is considered a big gravitational wave at Earth (where these gravitational waves are produced in the depths of the Universe, they are incredibly strong - strong enough to rip you apart) and therefore a rare one - so rare that we statistically didn't expect to see one in the amount of data we collected.  (Of course, the Advanced LIGO upgrade will change that!)

So, if we have yet to make a direct (meaning measured with our own instruments) detection of gravitational waves, how do we know that they really exist?  After all, this is a lot of effort and resources going into the search!  Well, we have seen the effects of gravitational waves on astrophysical systems in the Universe.

In the early 1970's, a pulsar (a very dense star that has beams of radio waves coming out of the magnetic poles) was discovered in the constellation Aquila at the Arecibo radio telescope in Puerto Rico.  The beam of radio waves passed over the Earth 17 times every second.  After observing this star for a while, it was discovered that some of the radio pulses came a little late and others a little early.  The periodicity of these arrival times indicated that the pulsar had a companion star and they orbited around each other (together, this system is known as PSR B1913+16 [referring to its sky coordinates]).  After further observation, it was found that the orbit of these stars around each other was gaining speed indicating that the stars are getting closer together (this is just like how a figure skater starts spinning with their arms extended at their sides and then, as they pull their arms to their body, they spin faster).  This can only happen if energy is being carried away from this system of stars.

The only energy loss that matched what the researchers, Taylor and Hulse, observed was the energy carried away by gravitational waves.  After about 20 years of making observations on this system, their measurements consistently matched the energy loss caused by gravitational waves.

This plot shows the change in the periodic time of closest approach (periastron) of this pulsar system compared to when the first observations were made in the early 1970's.  The red dots are observational measurements and the blue curve is the prediction from general relativity given the emission of gravitational waves.

This provided evidence of the existence of gravitational waves and won them both the 1993 Nobel Prize in physics.  Unfortunately, LIGO will not be sensitive to this particular pulsar system for about 300 million years even with upgrades to the detector.

Now that we know that gravitational waves really are out there, we want to detect them affecting our own instruments so that we can learn more about the sources that made them (after all, we know exactly what is going on for the source above).  Gravitational waves have encoded in them information about what made them very much like how radio waves can have music encoded on them.  Just like without a radio you can't hear the music, without detectors like LIGO, we can't learn more about what made these sources.  Gravitational waves can be emitted by things that don't produce light, like black holes, so we will be able to see them in ways traditional astronomy (astronomy using light) never can.  On top of all that, gravitational waves can travel through matter and emerge unchanged - basically, there is no such thing as a gravitational wave shadow!  So we will be able to observe things in the Universe that will forever be obscured to traditional astronomy.

***

Note that I have added 2 new pages (listed just below the blog banner): "Ask a Question!" and "Contact".  If you have a question you would like to ask, please fill out the form in "Ask a Question!".  If you would like to contact me, please fill out the "Contact" form.  Of course, you are more than welcome to leave comments to any blog post and start conversations with other readers!

Crawfish Boils and On the Road Again...

Last week's post came to you from the LIGO-Virgo Meeting in Boston, MA.  This week, it is coming to you from Atlanta, GA.  I just arrived here for the APS April Meeting.  My room is a beautiful corner room with two great views!  So I've chosen the better view from one of my windows:

Actually, I am here a day early so that I can attend the Professional Skills Development Workshop which is designed to improve the communication and negotiation skills of women physicists.  I'm looking forward to this as, while I would love to improve my communication skills, I really feel that I need to develop negotiation skills.  I am currently working to transition my current postdoc position (which is temporary by definition) into a more permanent position, not only because I love my work and the opportunities I have here, but my husband also works at the LIGO Livingston Observatory as an engineer.  The fact that I am this early in my career and living under the same roof with my husband, who is also happily employed in his field, is almost unheard of.  This is known as the two-body problem - when two academic professionals are challenged to find a way to find jobs together; I plan to write a blog post on this later.  That being said, I almost want to jump and any offer that can be scrapped together for me - the last thing I want to do is ruin the good thing I have going.  This is exactly one of the reasons that women tend to make less than men, even in physics - we undersell ourselves.  While I have no intention of trying to wring every penny I can out of a new position, I want to make sure that I am at least being compensated properly for my work.

As for the APS April Meeting, I will be giving a talk on the latest burst gravitational wave all-sky search results.  The information for my talk is here and the "plain English" science summary of the paper is here.  Once I give my talk, the presentation will be publicly available on the LIGO Document Control Center (DCC).  I will also be attending the APS Forum on Education Executive Committee Meeting and this will be the last of my term.  I have more than enjoyed the others I was privileged to serve with and it has been wonderful to get a chance to spread my wings a little more in physics education.  Of course, I have days and days of interesting talks and other activities to look forward to.  I will make sure to Tweet points of interest so make sure to follow me @livingligo.  You can also follow others' Tweets from the meeting using the hashtag #APSapril.

Between my trips to Boston last week and this one to Atlanta, I did get to be home in Baton Rouge for a few days.  Yesterday, the observatory staff was updated on the large scale status of the Advanced LIGO upgrade by the program leader, David Shoemaker.  While that was very informative (all is going well), the best part of the day of the crawfish boil we had outside afterwards.  For those of you who don't live in the American South (specifically the deep south), crawfish/crawdads/mudbugs/crayfish (but don't call them the latter around the natives lest you truly out yourself as not one of them) are essentially small freshwater lobsters that yield about the same amount of meat in their tail as a shrimp.  The meal takes "family style" to a new level: everything is served in heaps and you get a tray instead of a plate and it is heaped with the crawfish, sausage, corn-on-the-cob, and potatoes.  Oh yeah, and you don't get utensils.  This is a get-your-hands-dirty kind of meal.  Here is what my lunch looked like (before I started tearing the little critters apart - the communal aftermath from everyone at the table wasn't nearly as pretty):

This is considered a "dainty" portion.  A few other tips on how to fit in as a local:

• Don't sit while you eat crawfish - you stand so that the juice that can sometimes explode out of the body when you separate the tail from the head doesn't get all over you.
• Suck the heads!  Once your remove the tail, don't through away the top part of the body - that's where all the best flavor is.  As I have never done this myself, I am not sure if they are referring to the seasoned boil that remains inside or if they actually suck the "stuff" out.  To me, it just looks like the poor thing is trying to escape!
• Again, don't call them crayfish.

And a point of common sense - take your watch off!  Mine still smells like crawfish!

March LIGO-Virgo Meeting in Boston

So, I am at the LIGO-Virgo Meeting in Boston right now.  As you may (or may not) know, our two collaborations are very close knit.  We schedule our upgrades to be around the same time, we always share our data, and we collaborate on our science to get the most from our work.  Being a part of a big international collaboration is exciting and gives you a new perspective on international politics - in science they exist, but are much easier to deal with since we are all working for the same goal.

Here is the gorgeous view from my hotel window:

Personal Complexes:

Another thing about being one of over 800 scientists and engineers working on a project is that you can feel small.  I've written before about the Impostor Syndrome - when people who are fully qualified and competent feel inadequate.  Sometimes, these meetings bring those feelings back to me.  Every time someone comes to me and asks me what I do, I feel like my worth is being weighed.  But it absolutely isn't!  After all, I do the same thing to new colleagues that I meet and I am only interested in learning more about them and maybe working with them in the future.

I was starting to feel inferior while I was traveling here...  I was sitting at my gate during a layover and a colleague I consider a friend was sitting in his seat diligently working on his computer.  What was I doing?  Reading a vampire book.  The self-loathing voice in my head immediately chimed in with, "See, there is someone who is deserves the esteem of the collaboration.  He works hard and makes the most of his time.  What are you doing?  Reading a book about things that don't even exist!"  As I was resigning myself to mediocrity, he put his computer aside and started talking with me.  During our short conversation, he paid me the most unexpected complement.  I'm not going to repeat it here, but I was speechless and ecstatic at the same time and tried not to tear up.  I smiled and thanked him because his words forced me to think well of myself (not that I told him that).  If he is reading this, you know who you are and what you said even though you don't know how much it mattered to me - THANK YOU!

I've been trying to work more on these issues but I don't ever expect to completely get over feeling inferior to my peers.  Not that I really want to - I've met many scientists who thought they were a divine gift to science and I can't stand them (even if they are right)!

The Science:

The final data analysis from our last data run is finishing up and we've been talking about these results and preparing for the demands the MUCH more sensitive Advanced LIGO and Advanced Virgo detectors will place on our analysis infrastructure.  This has been a time of reorganization.  I gave a short talk about the functionality of the gravitational wave simulation software (called GravEn) I wrote while I was a graduate student.  This has been the standard software we've used to measure the sensitivity of of our burst data analysis methods.  We are also taking time to consider if there is a better way of doing it.  So far, it seems like GravEn is still the bee's knees and that makes me very happy!  (The science summary of the last burst data analysis paper is here.  The plots that show the sensitivity of our methods to different kinds of signals [the second and the third] were made using the simulations I produced.)

There have also been talks on the status of LIGO, Virgo, GEO, the Japanese KAGRA detector, and the status of what used to be the LISA space-based detector (this was a partnership between the ESA and NASA until budget issues forced NASA to cancel being a full partner).  There is progress being made on all of these fronts - even LISA (which is now led by the ESA and known as NGO for the New Gravitational-wave Observatory).  Every where you walk around the conference hotel, you see small groups working together on a project and a few very tall people in red uniforms (the Wisconsin Badgers are staying in our hotel for their NCAA Sweet 16 game tonight against Syracuse).

What Would YOU Like to Ask a LIGO Scientist/Engineer?

As part of a talk on the collaboration's outreach activities, this blog was featured!  (Those who don't know my science work will often still know me as the "Living LIGO Lady".)  It was also announced that I would like to feature interviews of gravitational wave people (scientists, engineers, etc.) on this blog.  When I originally started writing this, I wanted to make science human and accessible.  I feel like I am running out of human things about me to talk about (I'm not all that interesting).  But there are so many others with different backgrounds and stories that I would like to share with you.  I already have a list of questions I am thinking about asking (not all of them will be mandatory, of course) but I want to invite you to tell me what questions you would like to as a LIGO person?  Tweet them to me @livingligo or leave a comment here (below).  You can also email me at amber@livingligo.org.  I'm thinking of using my husband, a mechanical engineer for LIGO, as a Guinea pig (he can't cook and likes to eat, so I think I can convince him :P ).

Until next week!

Q: Are there really Vegas odds on GW detection?

@Astroguyz  asked:

Are there really Vegas odds on GW detection?

The answer to this is yes, there were Vegas odds on the detection of gravitational waves.

This story starts in latter half of August of 2004.  Ladbrokes created a special category of wagering based on successful scientific discoveries by 2010.  These were the discovery of life on Titan, a fusion (rather than fission) nuclear power plant, finding the Higgs Boson, understanding the origin of cosmic rays, and the discovery of gravitational waves.  Originally, the odds were set at 500:1.  Well, those of us in the know thought that the broker was way off and we had a lot to gain by taken them up on their offer - so many that the broker realized the same thing.  Within just a few weeks (I cannot find the exact date but the news articles I've read implied it's between 2 and 3 weeks), the odds were slashed from 500:1 to 100:1, 10:1, 6:1, then 2:1 before they finally closed the bets.  If I wasn't a broke graduate student in 2004, I even I would have jumped on these!

Here is some of the news coverage of the betting:
   26 August 2004 - New Scientist
   31 August 2004 - BBC News
   29 July 2010 - The Economist

If you read through these, you will note that the same LIGO Science Collaboration member is quoted: James Hough from the University of Glasgow.   I asked him about this in an email and he wrote:

"I think my bet was for 25 pounds at 100 to 1 but the chair of the UK oversight committee had 50 pounds at 500 to one.

Unfortunately as you know we did not succeed.

But you can imagine my excitement over the Big Dog event!!  I was on tenterhooks for weeks!"

As James notes (and as I have mentioned on this blog many times), LIGO has yet to make the first direct detection of gravitational waves.  In the end, Ladbrokes cleaned up.  I do hope that they open bets like this again though since I know that Advanced LIGO will be able to reach 1000 times more of the Universe than it did during its last data run in 2010 (when we started the aLIGO upgrades).  Instead of maybe seeing gravitational waves, we expect to be able to see tens of gravitational waves every year after aLIGO reaches its design sensitivity.  I can't wait!

If you are interested in making bets on odd things, Ladbrokes does still have a "Specials" category with all sorts of odd things you can wager on.  If you have a gambling problem, please consider contacting the National Council on Problem Gambling at 1-800-522-4700.

...

P.S.  As I wrote this blog post, it is to the horrible background music of uninterruptable power supplies (UPS) in my and neighboring offices beeping due to a power outage here at LIGO Livingston (loving my office with a window!).  This is when our computer staff really gets called into action - all of the computers that run the instrument AND the supercomputer that is located here need to be powered down before their UPS fails (they are only supposed to be good for minutes to give you time to shut down) and then they get to power everything back up again once the power is back on.  And there is an order to powering the computers back on!  So I guess this blog post comes to you today courtesy of my laptop battery :) 

The picture above is looking down on the large assembly area (not far from my office) where systems like seismic isolation are being put together for Advanced LIGO.  The lights that you see are emergency lighting so no one hurts themselves trying to leave in the dark.  This is a view I've never seen before.

First Software Engineering Run for Advanced LIGO

Most of the visible work on Advanced LIGO has been revolving around the installation of new instruments that are needed to increase the sensitivity of LIGO about 10 fold.  While this is exciting, it can feel a little like being on the outside looking in for data analysts like myself.  But there is still much to prepare for!

The first step in that preparation starts in a few days with the first Software Engineering Run (which we abbreviate ER1 - there's longish, boring story on why it isn't being called SE1).  The goal of this is to start testing our computing infrastructure and data analysis methods with simulated data (remember, Advanced LIGO is still not complete).  For this first run, we will be simulating the channels of data that would contain information about a gravitational wave.

But what is a channel?  Just like channels on a TV, LIGO has many different data streams called channels that report on basically everything involving the instrument.  Besides the channel that will carry information about gravitational waves, we also have channels of data from seismometers that tell us how the ground is moving beneath us, channels from microphones placed around the detector that tell us about loud noises like thunder that can cause vibrations in the detector, and channels that tell us how different places on a mirror inside of LIGO is moving (and we can combine channels like this to tell if the mirror is moving up, down, sideways, front to back, rolling, etc.).  This is just the beginning of the channels we record at LIGO (there are hundreds per detector)!  We use these to cancel out unwanted movement and to double check if a potential gravitation wave is real or caused by vibrations in our environment (we would be less likely to claim a detection around the time that our seismometers indicate a train moving on the tracks a few miles away from the detector here in Louisiana).

So, we are starting out small with ER1 and focusing on just the gravitational wave channels (with simulated gravitational waves included to give the detection software a workout).  In the future, more of the Advanced LIGO channels will be simulated and included in the run.  We plan on having about 5 or 6 of these runs until Advanced LIGO is ready to give us all of the channels for real.  But, the transition from Software Engineering Run to Engineering Run should be seamless.  Engineering Runs precede Science Runs to allow us to work out any bugs in the real detector before we start using the data for science purposes - but data from engineering runs is handled like it would be if it were science data.  As more subsystems in LIGO are installed and producing data, the simulated data for those channels will be replaced with real data.  The only difference between the last Software Engineering Run and an Engineering Run will be that none of the data is simulated anymore.

It is anticipated that, by having these ER runs, that the computational infrastructure for Advanced LIGO will be ready to handle the new demands of the more sensitive detector.  We are entering a new era in LIGO where detections will be expected on a fairly regular basis (once the detector has been tuned into its design sensitivity).  We need to be able to respond quickly to potential detections to alert others in the astronomical community and for us to vet the detection in a time efficient way.  We want to be able to clear detections off of the table, so to speak, before others become backlogged.  Honestly, I am excited at the prospect of this since I have worked with LIGO since it took its first science data and I remember collaboration meetings being focused on how to make the data clean enough that we could see more than just instrumental artifacts or environmental contaminants.  Now I'm thinking about backlogged detections!

LIGO has several supercomputer clusters and one of them is located right here at the LIGO Livingston Observatory.  So, I went downstairs (from my office) and took a few pictures of our cluster today:

Above is a picture of the computers facing the front of the room.  Since these computers produce a large amount of heat and noise, they are isolated in their own room which also allows for the efficient use of extra air conditioning (and noise containment).  This is an odd room to be in because of the noise but also because of strong air currents moving the heat around.  The wind is noticeable and it can change quickly between a warm breeze to a cold one as you walk.

This is a close look at the computers in the racks (as we call the large rectangular container).  Each one of the horizontal shelves is a computer.  Many computers are used simultaneously to search LIGO data for gravitational waves.

This is the back of the rack shown in the previous picture.  If you are ever chilly, this is the place to stand since the heat pushed through the fans from the computers is dumped here.