When the Universe Chirped - Detecting Gravitational Waves
When Joe Betzwieser found out that that a bright signal had been detected from the control room of LIGO Livingston, a Laser-Interferometer Gravitational-Wave Observatory in Louisiana, he was just glad that he wasn't working.
Just an hour or two before an instrument operator saw a squiggly wave run across a monitor in the LIGO control room, signaling gravitational waves or "ripples in spacetime" for the first time ever, Joe was making calibration measurements on the instrument. If he had been working at 4:51 a.m. central time on September 14, 2015, the "chirping" of two black holes colliding a billion years ago might never have been detected within the long tunnel "arms" of LIGO in Louisiana.
Update: Listen to the gravitational waves:
"I was making measurements on the instrument, actively affecting it," Betzwieser said when I interviewed him at a live announcement event today at LIGO Livingston. He is a research physicist at LIGO Livingston, and his work involves calibrating the laser-based gravitational wave detection instrument. His calibrations earlier the night of Sept. 14 would have interfered with the black hole merger signal that came across near 5 a.m.
Betzwieser has been looking forward to the day scientists might finally detect gravitational waves since 2001, when he become a graduate student at MIT. "I've been working on this in various forms for the last 15 years," he said. "We did it."
Joe Betzwieser giving a tour at LIGO. Photo by Paige Jarreau.
There are two LIGO detectors in the United States, one in Livingston and one in Hanford, Washington. Approximately 10 milliseconds after the Sept. 14 gravitational wave signal was detected by LIGO Livingston during a first engineering test, the exact same waveform showed up at LIGO Hanford. The facilities were constructed starting in 1994, with the very specific goal of detecting the ripples in the fabric of space-time predicted but never observed by Albert Einstein himself.
"Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot otherwise be obtained. Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. This collision of two black holes had been predicted but never observed." - LSU Press Release
Photo by Paige Jarreau.
Imagine that in space, a huge event like the merging of two black holes is like throwing a massive rock into a calm pond. As the rock sinks, you see concentric waves or ripples in the water spreading outward from the spot where the rock is now quickly sinking. The same thing happens around the black hole merger event. But instead of water waves, we see gravitational waves - deformations of space-time.
Being able to detect gravitational waves opens up for scientists a whole new window onto events in the universe that we can't "see" but could potentially "hear" via LIGO facilities. Betzwieser looks forward to the day when these signals will be "routine." But for now, he's just happy that not being a workaholic paid off big time.
Detection tunnels at LIGO Livingston.