Shortly after 8:41 a.m. EDT on Aug. 17, 2017, Fermi's Gamma-ray Burst Monitor detected a pulse of high-energy light from a powerful explosion, which was immediately reported to astronomers around the globe as a short gamma-ray burst. Less that two seconds earlier, scientists at the National Science Foundation's Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational-waves dubbed GW170817 from a pair of smashing super-dense stars, encouraging astronomers to look for the aftermath of the explosion. Shortly thereafter, the burst was detected as part of a follow-up analysis by ESA's (European Space Agency's) INTEGRAL satellite. NASA's Swift, Hubble, Chandra, and Spitzer missions, along with dozens of ground-based observatories, later captured the fading glow of the blast's expanding debris.
This is the first time scientists have conclusively detected light associated with a gravitational-wave event, thanks to two merging neutron stars in the galaxy NGC 4993, located about 130 million light-years from Earth. The figure shows an artist's impression of the aftermath of this merger.
Neutron stars are the crushed, leftover cores of massive stars that exploded as supernovae long ago. The merging stars likely had masses between 10 and 60 percent greater than that of our Sun, but they were no wider than Washington, D.C. The pair whirled around each other hundreds of times a second, producing gravitational-waves at the same frequency. As they drew closer and orbited faster, the stars eventually broke apart and merged, producing both a gamma-ray burst and a rarely seen flare-up called a "kilonova."
GW170817 showed astronomers that heavy elements found on Earth like gold, platinum, and uranium were likely produced kilonovae long ago.