Happy Halloween!

Wow!  I can't believe how long it has been since I've posted.  I've been horribly busy keeping up with teaching at LSU (and trying my best to make my lectures interesting), getting my LIGO work done (we are preparing for the 3rd software engineering run for Advanced LIGO [read about the first one here]), and some personal life complications that we all deal with from time to time.  I understand better why the blessing, "May you live in interesting times," is more of a curse.

So, to tide you over until my next full post (tomorrow), here is the feature presentation of the Science Education Center's monthly Science Saturday - Halloween Edition (2011):

Here, William Katzman (Science Education Center Lead) plays a laid back fellow with some paranormal explanations of "spooky phenomena".  I play a scientist who explains all of the phenomena in terms of science.  Before the day of the presentation, we decided what spooky phenomena we were going to use, but we never rehearsed the show - I'm surprised it turned out so well (if I say so myself)!

My New Jobs and Working in Academia

THE NEW JOBS

I've talked before about my current position as a postdoc (short for postdoctoral scholar/researcher/fellow/etc.).  This is a temporary position very much like a medical doctor's residency.  I've held this position for the past 5 years and I've loved it, so much so that I managed to land myself a more permanent position, or I should say positions since I now have 2 jobs.

My first job that will be replacing my postdoc (which is up at the end of the month) is "Data Analysis and EPO Scientist" for Caltech but working at the LIGO Livingston Observatory (EPO stands for Education and Public Outreach).  This is a half-time position that will allow me to continue my LIGO research and continue to perform outreach.  Basically, this new scientist job at LIGO will let me to keep doing what I've been doing for the last 5 years.

My second job is an instructor position in the LSU physics department.  This semester I am teaching conceptual physics (PHSC 1001: Physical Science) which is sometimes referred to as "physics for poets".  I am especially excited about teaching the class at LSU because many of the students are future teachers themselves.  I've taught the equivalent course to this while I was at Penn State (PHYS 001: The Science of Physics).  This was the one course I had complete control over while I was at Penn State: including text book selection, lecture & exam creation, etc.  I picked this class because it is hard to teach.  Through my previous teaching experience, I discovered that the less math you use in a physics class, the harder it is to teach.  Calculus-based physics is MUCH easier to teach than algebra-based; not because the students in the calculus-based physics class are smarter (which isn't true), but because a teacher can use math as a crutch and not have to truly articulate concepts.


THE GOOD AND THE BAD

I am really thrilled about my jobs.  Not only do I have a job (with benefits) in this economic climate, but it is in my field and doing what I love to do.  I am also back in the classroom which I missed (but loved the work in outreach I've been doing).  I get to continue doing to LIGO research.

In a sense, I have a very non-traditional "professorship" since I get to teach and do research.  The reason this isn't really a professorship is that I do not have the ability to earn tenure.  In academia, after a certain amount of time (usually 7 years) you are eligible for a promotion that makes you a permanent member of the faculty at the school.  In higher education, the evaluation criteria usually include the quality of your research (usually measured on the amount of grants you obtained and papers that you published), your teaching, and your service to the school and the profession.  At very big research schools, much more weight is placed on research; in smaller liberal arts colleges, teaching is often more important.  The fact that I am in a non-tenure track position is good in that I don't have to worry about obtaining my own research funds or publish stacks of papers and it is bad in that I am never going to have the security that tenure could bring me.  Of course, I have the option of leaving my current positions in the future and finding a tenure-track job (which isn't easy to do these days).

Another good aspect about my split position is that it think it is pretty hard to get laid off from two different jobs at the same time.  I guess that's a kind of job security...  I may not have tenure but it will be hard for me to be completely unemployed.

Ultimately, I am thrilled that two different universities are willing to claim me and I still get to do what I love...  It doesn't get much better than that!

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!

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!

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.

Q: How Does Einstein@Home Search for Gravitational Waves?

@umbonfo asked the following question:

What about the Citizen Science project Einstein@Home? I'm running it but I don't know which GW data it's analyzing.

This is a great question and there is so much I want to tell you all about that I am going to break this down into smaller questions:

What is Einstein@Home?

If you aren't familiar with Einstein@Home (read more, sign up), it is a screensaver that looks for gravitational waves in data collected by LIGO and other detectors like it.  Basically, users allow Einstein@Home to become part of a large supercomputer seeking gravitational waves but ONLY when the users are not using their computers.  How many times have you gone to bed at night and left your computer on?  If it doesn't have anything to do, it just sits there.  Einstein@Home gives it something productive to do that comes at no additional cost to the user.  Below is a screenshot of Einstein@Home as it is running on my computer.  It shows you where the two LIGO detectors are (the green and blue 'L' on the starsphere), where the GEO detector in Germany is (the red 'L') and where on the sky this program is looking for gravitaional waves right now (the orange cross-hairs).  To learn more about what you see on the screensaver, click here.

This is a screen shot of the Einstein@Home screensaver from my laptop just moments ago.

How does Einstein@Home get data?

Once you install the Einstein@Home screensaver, the central data servers (at the University of Wisconsin at Milwaukee) send a small portion of data to your computer for it to analyze.  Once your computer is done looking at that data, it sends a message back to the central computers telling them if there was a candidate gravitational wave in it.  Regardless of the result, 1 to 2 other computers also process the same data to make sure that they all get the same results (and we are sure that there isn't someone out tampering with the software to report false results).  If the same results are found and there is a candidate gravitational wave in the data, then it is looked at more closely by physicists who specialize in data analysis (like me - although I look for different kinds of gravitational waves than Einstein@Home looks for).


What kind of gravitational waves does Einstein@Home look for?

Einstein@Home looks for a very specific kind of gravitational wave call a continuous gravitational wave.  The are expected to be emitted by rapidly spinning, dense objects like neutron stars.  If there is even a small imperfection in the spherical shape of these stars, they will be constantly emitting a gravitational wave (if you were to put the signal of the gravitational wave through speakers, it would sound like a single tone).  We look for this kind of gravitational wave by breaking down the data collected from the detector into its different wave components.  Think of the data as the sum of a collection of many different waves each with a constant frequency.  We can then take a chunk of data and break it up into its component waves.  (This is called a Fourier transform.)  Since we know what a continuous wave should look like, Einstein@Home then inspects each of the component waves to see if it could be a gravitational wave.

Does Einstein@Home do anything else?

Why, that's insightful of you to ask!  :)  Einstein@Home also processes data from the Arecibo radio telescope looking for pulsars - a special kind of neutron star that emits radio waves from their magnetic poles.  Every time that the star spins its jet of radio waves across the Earth, radio telescopes can detect it.  The data analysis in not quite the same as when Einstein@Home looks for gravitational waves, but the basic process of breaking down the data into its component waves is the same.

Why is Enstein@Home interested in discovering pulsars?

Knowing more about where pulsars are in our universe lets us know better where to look for them in our gravitational wave data (notice that the screensaver has crosshairs that show you specifically were Einstein@Home is looking for gravitational waves) and, since pulsars are a special kind of neutron star, we can get a better sense of how many of them are out there in the Universe which give us more accurate measures of how often we should expect to detect gravitational waves from them.

What has Einstein@Home found?

Well, since there has been no direct detection of gravitational waves yet, it is obvious that Einstein@Home has not produced a real gravitational wave yet.  However, it has found over 10 previously unknown pulsars including the fastest known spinning pulsar!

All of this would not be possible without users like you!  When all of the computing power of Einstein@Home is combined, it is within the top 20 or so supercomputers in the world!   


I hope I answered at least most of your questions about Einstein@Home.  As always, feel free to ask me questions by leaving a comment on this blog or tweet me @livingligo.

About Time...

I know that I haven't been posting as much as I usually do (I like to post once a week) but life gets in my way.  For example, I had a tooth break that needed fixed and both my husband and I have come down with the cold that has been making its way around the observatory.  Basically, between life and getting work done, I haven't had a lot of time.

But today is an important day since we will reach GPS time 1,000,000,000.  This time is measured in seconds from Sunday January 6, 1980 at midnight UTC (this is the official time of the planet measured at the Prime Meridian passing through Greenwich, England) without any leap second corrections to match the rotation of the Earth (astronomers use a similar time keeping method called Julian Date which is the number of days since January 1, 4713 BC without any corrections for outright changes to the calendar [like to the Gregorian calendar - which is the calendar we use today]).  Here at LIGO, this is important to us since this is how we measure the official time for everything and this time needs to be very accurate since we will never believe a potential gravitational wave detection unless it is measured at different observatories within the time it would take a it to travel between the sites - for the two LIGO observatories, the maximum time is 10 milliseconds.

Other than it being cool to watch the time roll over to one billion (like watching your car odometer roll over to 100,000 miles) this event can cause issues with the data analysis programs that we write to search for gravitational waves.  For example, I wrote a software package while I was in grad school that we still use to produce simulations to test the efficiency of data analysis software.  My baby is called GravEn (for GRAVitational-wave ENgine) and uses the GPS time to determine where the simulations will be added to the real data (this data with fake signals is never saved together so that we don't trick ourselves into thinking we saw something real).  GravEn has specifications in its programing to return the time of the simulation in whole GPS seconds in one column of the log file and the nanoseconds after that time in another column.  I have made it so that the whole-second time is returned with 9 digits and this is now an issue since the time will be 10 digits.  It is easy enough to fix, but it must be fixed!

This new 1,000,000,000 time is not going to be of any serious concern like people feared the Y2K bug to be.  Instead, all of us code monkeys (as computer programers are lovingly referred to) need to go back and make sure that we allow enough (10) digits in the parts of our programs that use GPS time.

So, GPS 1,000,000,000 will happen today (September 14) at 1:46:25 UTC (or September 13 at 9:46:25 PM in Eastern Daylight Time).



***

My next blog post will be on Thursday and will answer the reader question on exactly what kind of gravitational waves Einstein@home seeks and how it looks for them.

The "Big Dog" in the Envelope

So, there has been a lot of excitement in the LIGO and Virgo Collaborations because we thought that we may have had a gravitational wave detection candidate from the early morning hours of 16 September 2010.  Because the potential source was localized in the vicinity of Canis Major constellation, the candidate event was informally dubbed the "Big Dog" (get it? we think we're cute).

I was especially excited since I was one of the first people to know about the event.  I mentioned in a previous blog entry that LIGO and Virgo have developed an effort to process the data that we collect rapidly so we can tell our traditional astronomy colleagues (those with actual telescopes) where to look for a potential optical signal component of the event.  I was one of about 25 scientists that were notified when a candidate event for observation was detected so that we can make sure that the event is valid before we send it out for observation.  While I wasn't the scientist on duty for this purpose at the time, I received the text message a little after 1 AM Central time (I couldn't sleep).  This was only 8 minutes after the data was collected!

It was sent out for observation and the entire collaboration began to get very excited.  This looked just like what we would expect from a neutron star-black hole binary (pair) system orbiting into each other (to make a bigger resulting black hole).  But one of the things that every scientist needs to learn is not to get overexcited and declare this to be the first direct detection of gravitational waves without making sure that this isn't a false alarm.  There are 2 ways this could be a false alarm:  1:  There is something in the environment that just so happened to make a coincident signal in all of the detectors (LIGO in Louisiana, LIGO in Washington state and Virgo in Italy) or 2:  This could be a blind injection (test).  Until we knew for sure, no one was allowed to discuss this event outside of the collaboration.  I've had to keep my lips sealed for 6 months (just like the over 800 other scientists who are in the Collaboration)!

A blind injection is a test the higher-ups in LIGO can do to make sure that the data analysis methods are doing what they need to be doing.  Basically, a very small subset of people in the collaboration (think like 2 or 3 people) inject a fake signal into the detector and this injection is not recorded anywhere like the other injections we regularly do to test things like detector calibration, etc.  The fact that a blind injection exists is sealed away (in what we metaphorically call an envelope) until all due diligence is done and the collaboration is ready to declare that the signal is a detection unless it is a blind injection (that it, we prove that it is nothing in the environment or and nothing was wrong with the detectors detectors that caused the signal).

Yesterday (14 March 2011) at the LIGO-Virgo Meeting was the big day when we opened the envelope (which turned out to be a flash drive with a PowerPoint presentation on it).  If the envelope was empty or if whatever injections were in the envelope were not the "Big Dog", then that would mean we made a detection.  The envelope was opened and, indeed, the "Big Dog" was inside and not a real gravitational wave detection.

I was not surprised - there had not been a blind injection in the run before this and everyone expected that there would be at least one.  However, there was also a big part of me that was hoping against hope that this was real.  My entire career has been dedicated to the effort of directly detecting gravitational waves and the development of gravitational wave astronomy.  If the "Big Dog" had been real, this would have been a fulfillment of the first part of my goals and the opening of the door of the second part.

Regardless, all of the effort that was put into validating the "Big Dog" up until it was revealed to be a blind injection has been a priceless exercise for the collaboration.  We even have a paper that was ready to be submitted for publication if it had been real.  Since this is something that we have never done before, we have developed skills for when we do make the first detection with Advanced LIGO. 

Below is a picture (from my seat) of the title slide in the presentation opening the envelope.  This just goes to show that even if you think that scientists are smarter than you, it all depends on how you define smrt :)

7 April 2011 - UPDATE:  Read more detail on the "Big Dog" blind injection here!

This Past Week

This week I've done both outreach and science.  If you aren't familiar, outreach is working to bring science to people who don't do science for a living; to educate the public.  This is a particular passion for me (hence this blog) since outreach lets me share my excitement for what I do with people who are interested.  It lets me remind myself of why I do what I do everyday.  Let me give you an example: looking for gravitational waves is getting the chance to discover something that no one has ever gotten to directly detect before (not that I am the only scientist looking for gravitational waves [I will do a post on the large LIGO-Virgo collaboration later] and we do know that gravitational waves exist [the 1993 Nobel Prize in Physics was awarded for the proof]) which is very exciting, but there is a huge amount of detailed work, that can sometimes seem removed from gravitational waves, that needs to be done to reach that goal.  That means, that sometimes I sit in my office and think, "Why am I so concerned about X?  This doesn't feel like it is going to make a difference."  That's when you need to take a step back from the work and see where in the big picture your work fits in.  Then I feel my motivation return.  But when I get to do outreach, I get to share what I do with someone who may have never heard about gravitational waves before.  I get to see the awe in gravitational waves that sometimes get buried in the daily work that needs to be done.  When I do outreach, I return to my desk with a vigor that I would have not had otherwise.

Last Saturday, I came into the observatory to give a tour to about 25 first year physics students from Tulane University in New Orleans.  Since I don't get to work with college students much, this day went a little differently than when I work with middle or high school students.  The questions are sometimes a little deeper (I say sometimes because you would be surprised at the insight that a 5th grader can demonstrate) and I don't need to rephrase my responses as much (meaning that I can sometimes use the big words without explaining them).  The one thing that is always the same no matter if the group is middle/high school, college, or public is that when they get to explore the exhibit hall in the Science Education Center everyone becomes a kid again.  Everyone darts from exhibit to exhibit for the first 5-10 minutes until they find one that really catches their attention and then they start experimenting on deeper levels.  I often tell groups the best part about my job is that I have a key to the Center and I know how to turn all the exhibits on (and it is the truth).

Then on Wednesday and Thursday I got to give tours of the observatory to middle school students.  The most rewarding part of working with these groups is hearing the students talk amongst themselves about how they want to work as a scientist or engineer someday.  Hearing that reminds me of when I was their age and dreamed of being a scientist.  That really makes going back to your office and doing all of the details that need to be done easier - I get to live my dream.

So, what kind of science did I do this week?  Well, I specialize in creating computer programs that go through the enormous amounts of data we take everyday to look for gravitational waves in the sea of noise that comes out of our detector.  That means that many of my issues I need to work through involve computer programming and statistics (I hope you can see now why sometimes I lose sight of the bigger picture).  To that end, I am also a 'librarian' for the computer programs that are written in MATLAB in the LIGO-Virgo Collaboration; this library is called MatApps.  I work with others from Penn State to help keep MATLAB easy to use for the collaboration and to help keep the programs we have written in a central location.  So, this week I spent time working on a tool to make it easy for MatApps users to use the programs it contains.

I also worked on reviving a project that I started about 2 years ago that will help us evaluate if any candidate gravitational waves are real by checking that the measurements are physically possible based on the detection time difference between each detector and the strength that each detector saw the signal.  I am reviving this so that I can collaborate with a friend to tailor this to the needs of the physicists that look for gravitational waves from two stars or black holes rotating around each other and merging to become one (I specialize in looking for short duration gravitational waves from unknown or unmodeled sources call bursts).  We also hope to write of the results of this work and publish it in a scientific journal.

Outside of some doctors appointments (I've had recent troubles with a kidney stone that clogged up the works), this was pretty much my week.