What happens when two neutron stars collide?

The answer

Neutron star mergers are among the most energetic events in the universe. On August 17, 2017, LIGO and Virgo detected gravitational waves from GW170817, a neutron star merger 130 million light-years away in galaxy NGC 4993 - the first event observed in both gravitational waves and electromagnetic radiation. The collision produced a kilonova, synthesizing approximately 16,000 times Earth's mass in heavy elements through rapid neutron capture (r-process) nucleosynthesis, including an estimated 10 Earth masses of gold and platinum. The merger emitted a short gamma-ray burst lasting 1.7 seconds, followed by ultraviolet, optical, infrared, X-ray, and radio afterglows observed by 70 telescopes worldwide. The event confirmed that neutron star mergers, not supernovae, are the primary source of heavy elements like gold, platinum, and uranium in the universe. It also provided an independent measurement of the Hubble constant and confirmed that gravitational waves travel at the speed of light.