Over a century ago Albert Einstein predicted the existence of gravitational waves, and last year they were finally detected.
The National Science Foundation (NSF) detected the gravitational waves at its Laser Interferometer Gravitational-Wave Observatory (LIGO). The observatory, which is actually a pair of observatories based in Hanford, Washington and Livingston, Louisiana, recorded the gravitational waves produced by the merging of two black holes.
“We have detected gravitational waves. We did it,” executive director of LIGO, David Reitze said at a press conference at the National Press Club on Thursday.
Reitze and his fellow scientists looked at the convergence of two black holes, one with the mass of 29 suns, the other with the mass of 36 suns, to find their gravitational waves. The two black holes came together 1.3 billion years ago, after spiraling towards each other at half the speed of light. The resulting waves have been traveling through the universe ever since.
Scientists at LIGO detected the waves on September 14, 2015. Gravitational waves, which are basically a wrinkle in space-time, are essential to Einstein’s general theory of relativity.
The waves are incredibly small, which is why the LIGO was needed to measure them. The waves put off from the merging of two black holes were about one-thousandth the size of a proton.
“The total power output in the gravitational waves during the brief collision was 50 times greater than all of the power put out by all of the stars in the universe put together,” LIGO co-founder Kip Thorne said at the press conference. “It’s unbelievable. Because it was so brief, the total energy was not that big, it was ‘only’ what you’d get by taking three suns, annihilating them and putting them into gravitational waves.”
In addition to proving Einstein’s theory correct, gravitational waves prove the existence of black holes. Up until the detection of the waves, which would need enormous events to be created, only the after affects of a black hole had been viewed by scientists.
“What was amazing about this signal is that it’s exactly what Einstein’s theory of relativity would predict for two big, massive objects like black holes, spiraling and merging together,” Reitze said.
To measure such anomalies, each LIGO observatory has a two and a half mile long vacuum tube in the shape of an L. A laser beam is fired down the distance of the tube, reflecting off mirrors that make each beam almost 1,000 miles long. The beam then bounces back and is measured by extremely sensitive sensors that record any changes to the length of the beam.
The stations are separated by nearly 2,000 miles to ensure that any recorded events are not caused by local occurrences, such as earthquakes, which can potentially vibrate parts of the LIGO and give a false reading.
The event that occurred last September is exactly what scientists had been hunting for. The gravitational waves stretched Earth (and everything else they passed through) an indiscernible amount in one direction, and compressed it in a perpendicular direction. The stretching and compressing was so small that only the LIGO was able to record it.
In response, the White House Office of the President tweeted, “I’d like congratulate @NSF researchers at #LIGO for confirming #gravitationalwaves 100 years after Einstein predicted it.”
“Four hundred years ago, Galileo turned a telescope to the sky and opened the era of modern observational astronomy. I think we’re doing something equally important today, I think we’re opening a [new] window on the universe, a window of gravitational astronomy,” Reitze said.
Image Credit: Artist’s Impression of Gravitational Waves by R. Hurt/Caltech-JPL