LIGO Discovers Binary Black Hole Merger

On February 19, 2016, a crowd of MIT students, faculty, staff, alumni, and friends formed a long line around Building 26. A century after Einstein first predicted the existence of gravitational waves, they were eager to hear a panel of MIT LIGO scientists explain how they had at long last detected them. 

The panel, hosted by the Department of Physics and the MIT Lecture Series Committee, began with Professor Emeritus Rai Weiss, who gave a history of the LIGO project in its earliest days of designing and building interferometer prototypes. For Weiss and his students, the freedom and space to be found at MIT were important to getting the project off the ground. The group divided its time between working in the ramshackle but spacious Building 20, where Weiss said “you could do anything you pleased,” and hashing out ideas at the F&T Diner, once located where the Kendall T stop now exists. 

“Much of the LIGO project got invented at the roundtable,” Weiss said. “At that roundtable, you had beer and you had coffee, and you had hot pastrami. It was just wonderful—and it was very conducive to making things happen.” 

Weiss was joined by Professor of Physics Edmund Bertschinger, who gave the audience a refresher on the basics of general relativity and the significance of the detection of gravitational waves, as well as by MIT Kavli Institute research scientists Salvatore Vitale and Lisa Barsotti, who talked about the technical aspects behind the gravitational wave detection. Barsotti played recordings of the “whoop” produced by the merging black holes and described the seemingly impossible precision required to hear it. The “whoop” translates to a disruption within the laser interferometer of a mere 4 x 10-18 meters, or about 1/200th the size of a proton. 

“This is incredible, what we want to measure,” Barsotti said. “Every time I think about this—like, wow! We are superheroes! How can we really do this? It’s incredible!”

Matthew Evans, Assistant Professor of Physics, concluded the panel by looking forward to the future of the LIGO project. LIGO achieved its gravitational wave detection operating at only one-third of its full capacity. When LIGO scientists bring the observatory to its full capacity, Evans predicts that we will be hearing about binary black hole mergers frequently in the future – around 50 every year. Although future gravitational wave detections will no longer be front-page news, Evans is excited at the prospect of learning more and more about a now-audible universe. 

“The silent movie is over,” Evans concluded. “We’ve now got sounds from the stars.”