Diagram showing how light and gravitational waves were detected after the merging of two neutrons stars causing an explosion, called a kilonova. On 17th August 2017, NASA's FGST (Fermi Gamma Space Telescope) first identified a gamma-ray burst from the kilononva in galaxy NGC 4993, located 130 million light years away in the constellation Hydra. LIGO and the Virgo detector observed gravitational waves from the two stars merging 1.7 seconds before the Fermi gamma-ray burst occured. Scientists analysing gamma ray data from ESA INTEGRAL spacecraft also saw the gamma-ray burst from the kilonova. This is is the first neutron star collision to be detected.