![\"Alan](\"https:\/\/uwm.edu\/news\/wp-content\/uploads\/sites\/41\/2016\/02\/LIGOfaculty_h.jpg\")
Joining Brady in the quest are faculty members Jolien Creighton, Xavier Siemens and Alan Wiseman, along with 26 51ÁÔÆæ students and scientists. The 51ÁÔÆæ team is part of the LIGO Scientific Collaboration, an international consortium of 70 institutions and hundreds of researchers.<\/p>\n
\u201cThe 51ÁÔÆæ group has been a key part of the project from very early on,\u201d said Clifford Will, a distinguished professor of physics at Florida State University who is known for his contributions to the Einstein’s theory of general relativity. \u201cThey were involved both in building the infrastructure and in resolving issues related to using the data. They were responsible for important calculations that were used to make the detection. Some of those formulas were built into the data-analysis protocol for LIGO.\u201d<\/p>\n
Anticipating a meaningful signal<\/h3>\n
Einstein saw space and time as a continuum and gravity as a curvature of that space-time. Like a bowling ball placed on a bed creates a deep indentation in an otherwise flat mattress, so massive objects like stars warp space-time. Their movement creates gravitational waves.<\/p>\n
Hunting the elusive waves involves collecting measurements at two U.S. detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO), which feed copious amounts of data to several supercomputer clusters around the world, including at 51ÁÔÆæ.<\/p>\n
Each LIGO detector has two perpendicular arms that extend 2.5 miles from a central station, each with a mirror at the end. A laser beam is split, with half traveling down each arm and reflecting back off the mirrors. When a gravitational wave passes, it stretches one arm while squeezing the other in an alternating pattern. This causes tiny mismatches in the beams\u2019 round-trip travel time. The detector records this mismatch as an electrical signal which scientists sift through to identify gravitational waves.<\/p>\n
To distinguish gravitational waves from millions of other events that also upset the beams\u2019 arrival times, scientists calculate what the signal ought to look like for certain cosmic events \u2013 like the merger of two black holes, which scientists predict will cause the strongest waves.<\/p>\n
Brady\u2019s main contribution to the LIGO Scientific Collaboration was providing the framework to look for signals in the sea of data.<\/p>\n
Brady, who has devoted his academic career to studying black holes, became directly involved in the LIGO search while at Caltech on a post-doctoral fellowship in the mid-1990s. Wiseman and Creighton were doing research there at the same time. Brady joined the 51ÁÔÆæ faculty in 1998 and was present at the LIGO detector in Hanford, Washington, when it first took science data in 2002.<\/p>\n
\u201cBack then, we were inventing the methods to search that much data and inventing the computing methodologies to analyze it,\u201d he said. \u201cIt hadn\u2019t been done before.\u201d<\/p>\n
Advanced LIGO<\/h3>\n
Between 2002 and 2010, the observatories found no signals that indicated a gravitational wave. They shut down for a five-year upgrade to increase their sensitivity and began operating again in September 2015.<\/p>\n
Within days, Advanced LIGO, as the facilities are now called, uncovered a signal that scientists quickly identify as a gravitational wave.<\/p>\n
\u201cWe were involved in the pre-run stage \u2013 the dress rehearsal \u2013 when the signal arrived and we had to stop what we were doing and begin analyzing,\u201d Brady said.<\/p>\n
The discovery is described in a Feb. 11 article in the journal Physical Review Letters<\/em>. Twenty of the more than 1,000 scientists listed as authors were from 51ÁÔÆæ.<\/p>\n Brady didn\u2019t expect black holes to cause the first detection.<\/p>\n \u201cWe\u2019ve never seen a pair of black holes before. This was the example that we all thought of as being the beautiful result of our experiment. We all hoped for it, but we never thought it would be the first thing we saw.\u201d<\/p>\n The LIGO instruments also allow scientists to convert the gravitational wave signals into sound waves so that astronomical events can be heard.<\/p>\n When two black holes merge, for example, a \u201cchirp\u201d or \u201cwhirl\u201d represents the spiraling together of the holes just before they collide.<\/p>\n \u201cThe spiral can go on for tens of thousands of years,\u201d Brady said. \u201cThe sound we hear is the identifying signal of the last few seconds of the process.\u201d<\/p>\n 51ÁÔÆæ postdoctoral researcher Sarah Caudill experienced this first-hand.<\/p>\n \u201cWe knew within three minutes that the detectors had seen something,\u201d said Caudill, who ran the analysis that confirmed the signal came from two black holes.<\/p>\n \u201cSomeone made a time-frequency spectrogram and when I first saw those plots, my heart skipped a beat. We are all trained to look for the chirp-like signature of a real gravitational wave in the spectrograms. And these showed a beautiful textbook example of a chirp signal.\u201d<\/p>\n The LIGO group at 51ÁÔÆæ has been supported with sizable grants from the National Science Foundation. 51ÁÔÆæ has received nearly $29 million for the project in the past decade, with part of it going toward the construction and operation of a supercomputer cluster in the Physics Building.<\/p>\n Wiseman and Bruce Allen, who is now director of the Max Planck Institute for Gravitational Physics in Germany, were the main architects of 51ÁÔÆæ\u2019s computer hardware.<\/p>\n Computing power was expected to be a critical need from the start, and construction of the cluster at 51ÁÔÆæ began about the same time as the LIGO Scientific Collaboration formed in 1997, Wiseman said. Today, the 51ÁÔÆæ cluster is one of several that comprise the LIGO Data Grid, the network of supercomputers needed to scour the voluminous data accumulated in the search.<\/p>\n \u201cA well-established gravity research group at 51ÁÔÆæ put us in a good position to make computing contributions by the time the collaboration formed,\u201d Wiseman said.<\/p>\n For example, once LIGO data is recorded digitally, it\u2019s transported to many computing locations. 51ÁÔÆæ scientist Scott Koranda developed the method now used to replicate the data so it can be sent to multiple sites.<\/p>\n Creighton is the principal investigator of 51ÁÔÆæ\u2019s LIGO scientific research grant. Interpreting what gravitational wave signals tell us about the universe is one of his interests.<\/p>\n For him, LIGO is a family affair. Creighton and his younger brother, Teviet, share an interest in astronomy and physics, particularly gravitation. Jolien went to the University of Waterloo for graduate school to study quantum gravity, while Teviet headed to Caltech to work under Kip Thorne, co-founder of the LIGO facilities.<\/p>\n \u201cToward the end of my graduate work, I became more interested in gravitational waves,\u201d Creighton said. \u201cI went to Kip\u2019s group as a postdoc so I overlapped with my brother, who was also with the LIGO project there.\u201d<\/p>\n The 51ÁÔÆæ physicists and their collaborators \u2013 many of them former students \u2013 also developed and implemented the analytical tools needed to retrieve gravitational wave signals from the LIGO data.<\/p>\n \u201cThe [detector] delivers an electric signal that\u2019s related<\/em> to a gravitational wave signal, but you need to calibrate the data to see it,\u201d said Siemens, who co-chaired the LIGO Scientific Collaboration\u2019s Calibration Team.<\/p>\n Calibration is the first part of the data handling system created at 51ÁÔÆæ, which also serves as the alarm system that notifies project members when the instruments have detected a signal worthy of closer examination.<\/p>\n Promising data is uploaded to a database and team members around the world are notified. At that point, a painstaking process begins to verify the discovery.<\/p>\n The team has automated the initial process and can upload a candidate within minutes of acquiring the signal. The verification, however, might take weeks, or even months.<\/p>\n Advanced LIGO\u2019s first data-collection ended in mid-January, and the scientists have not yet analyzed the full dataset, so more detections from the first run remain a possibility.<\/p>\n This wouldn\u2019t surprise Wiseman who noted that Advanced LIGO was designed to be so sensitive that if it didn\u2019t detect an event, that information would be just as significant. It would mean their theories could be wrong.<\/p>\n \u201cGravitational waves will turn out to be the only way to uncover some cosmic phenomena,\u201d he said.<\/p>\n 51ÁÔÆæ is leading the charge to help develop the new branch of astronomy that gravitational waves have opened. Siemens heads a consortium of 11 U.S. research institutions that are monitoring millisecond pulsars to find and study the waves.<\/p>\n Pulsars are rapidly spinning, super-dense remains of dying stars that emit beams of light like lighthouses. As the regularly timed beams pass by Earth, scientists expect them to be disrupted by gravitational waves. The consortium, called the NANOGrav Physics Frontiers Center, is backed by $14.5 million from the National Science Foundation.<\/p>\n Just as the gravity center established by Leonard Parker and John Friedman molded the current faculty working on LIGO, Brady, Wiseman, Creighton and Siemens are educating the next generation of scientists.<\/p>\n \u201cPerhaps 10 percent of people in the LIGO project have worked and studied at 51ÁÔÆæ as students or postdocs,\u201d Siemens said.<\/p>\n One student is Alex Urban, who was at the LIGO detector in Louisiana as part of a fellowship when the signal was found.<\/p>\n \u201cI had a hard time thinking of it as something real,\u201d said Urban. \u201cNo matter how much you work on it, until you make a discovery, it\u2019s just an abstract thing in your mind.\u201d<\/p>\nNumber crunching<\/h3>\n
Interpreting the reams of data<\/h3>\n
What\u2019s next?<\/h3>\n