On Thursday, researchers announced the first-ever detection of gravitational waves, ripples in space-time whose existence Albert Einstein predicted 100 years ago. The discovery confirms not only a prediction of Einstein’s theory of general relativity but also the nature of black holes, and gives astronomers a new tool for observing the cosmos.
“We did it,” said a beaming Dave Reitze, executive director of the Laser Interferometer Gravitational-Wave Observatory (LIGO), via a live broadcast from the National Press Club in Washington, D.C. The waves are the result of the collision of two black holes that occurred 1.3 billion years ago, Reitze said. The announcement confirmed rumors about the discovery that had been swirling for several weeks.
The infinitesimal signals produced by gravitational waves were picked up using LIGO’s two identical L-shaped interferometers, one in Louisiana and the other in Washington state. The detectors each have two four-kilometer-long arms housing lasers and mirrors that vibrate in response to the stretching of space due to passing gravitational waves.
The researchers who operated LIGO, based at Caltech and MIT, observed the first gravitational wave signal last September, and then subsequently detected at least three more. The signal was converted into audio waves so that the team could “listen” to the black holes spiraling toward each other and eventually colliding.
The discovery follows an indirect detection of gravitational waves in 1974, when two astronomers from the University of Massachusetts, Amherst, used a radio telescope to observe a pair of rapidly rotating celestial objects known as a binary pulsar. The rate at which one of the objects emitted radiation matched what was expected according to Einstein’s theory. That observation earned those researchers the 1993 Nobel Prize.
In 2014, scientists reported observing signs of primordial gravitational waves created by the big bang, but the team later backed off the claim.
Gravitational waves will serve as a new tool for probing the secrets of the universe, in addition to more conventional means of observation, like visible light, X-rays, and infrared. The discovery opens “a new window of astronomy,” said Reitze. The researchers say it can be thought of like the end of the silent movie era, but for astronomy. “Up to now we’ve been deaf” to gravitational waves, Reitze said. “We are going to hear more from these things, including things we never expected.”