The discovery of gravitational waves last year sent ripples through the entire field of physics. They confirmed that space does indeed behave as a substance, which can be stretched and squeezed, as predicted by Albert Einstein’s theory of general relativity. They also ushered in a new era of astronomy.
In 2017, scientists detected gravitational waves from an event that was also observed by telescopes: Around 130 million years ago, two neutron stars spiraled toward each other and fused together — a phenomenon known as a kilonova. The rapidly rotating stars whipped up gravitational ripples in space itself. On Aug. 17, the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and advanced Virgo observatories on Earth detected those ripples. Because the waves were generated just as the stars merged, the scientists who detected them had enough time to alert astronomers of the light and radiation that would soon follow. [Related: The Greatest Space Science Stories of 2017]
The Laser Interferometer Gravitational-Wave Observatory, or LIGO, can find black hole binaries — a pair of black holes that are bound by gravity — as they spin toward each other and violently merge into a single black hole. LIGO consists of two L-shaped detectors with 2.5-mile-long arms, one in Hanford, Wash., and the other in Livingston, La. When a gravitational wave passes through the detectors, squeezing one arm and stretching the other, a finely tuned system of lasers and mirrors inside the arms can pick up those infinitesimally tiny distortions.
Since finding its first black hole merger in September 2015, LIGO has announced the discovery of several more black hole mergers, as well as a merger of two neutron stars — some of which the European Virgo detector picked up as well.