On 17 August the Laser Interferometer Gravitational-Wave Observatory (LIGO), along with sister observatory Virgo, detected a swell of gravitational waves. Less than two seconds after that signal ceased, the Fermi Gamma-Ray Space Telescope identified a flash in the southern sky. Though it would take several hours to verify, researchers had spotted a gamma-ray burst (GRB) triggered by the collision of two neutron stars.
In the ensuing weeks, 70 telescopes in space and on the ground collected data across the electromagnetic spectrum on the GRB, which occurred about 130 million light-years away in the elliptical galaxy NGC 4993, located in the constellation Hydra. The discovery, announced Monday at a Washington, DC, press conference and in some 50 scientific papers, has implications that stretch far beyond gravitational-wave astronomy. It proves that at least some short-duration GRBs are triggered by crashing neutron stars. It offers evidence of the tidal forces that rip the ultradense orbs apart and that the subsequent explosion creates heavy metals such as gold, platinum, and uranium. It even provides a novel means of measuring the universe’s expansion rate. Overall, the discovery sets the standard for how gravitational-wave and electromagnetic observatories can work in tandem to probe the universe’s densest and most energetic objects.
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