We just turned the volume up on the sky. Gravitational waves, the booming echoes of massive objects moving all over the universe, have been detected for the first time by LIGO, the Laser Interferometer Gravitational-Wave Observatory, which was recently upgraded.
Gravitational waves are predicted by Einstein’s theory of general relativity, which says that massive objects warp space-time around them. When these objects accelerate, they make gravitational waves: ripples in the fabric of space-time that spread outward, like the wake left behind a boat.
We have been pretty sure they exist for a while – their presence was inferred indirectly as far back as 1974 – but none had been observed directly.
In a press conference today at the National Press Club in Washington DC, which was simultaneously broadcast to the media and other members of the team that made the discovery, the LIGO collaboration announced that they had finally caught a wave.
“Ladies and gentlemen, we have detected gravitational waves,” said David Reitze, the executive director of the LIGO Laboratory, at the press conference. “We did it!” The announcement accompanies a paper published in Physical Review Letters.
This historic signal was produced by a pair of black holes roughly 1.3 billion light years away, one 29 times the mass of the sun and the other 36 times, orbiting each other and then merging into a single black hole.
LIGO’s dual detectors, based in Hanford, Washington, and Livingston, Louisiana, felt the tremors on 14 September 2015 at almost the same instant. Their sensors registered space-time expanding and contracting by as much as a thousandth of the size of a proton – a tiny distance, but 10 times larger than the smallest unit LIGO can measure.
This was a doubly lucky find: officially, the experiment wasn’t scheduled to begin taking data until four days later, on 18 September, in a run that continued until 12 January 2016. The signal arrived while the detectors were in “engineering mode”, making sure the instruments were running smoothly.
Read more: New Scientist