The merger of two neutron stars or a neutron star and a black hole. A kilonova produces a gamma-ray burst and is a strong source of gravitational waves. Many of the heavier elements in the periodic table, such as gold and platinum, are created in kilonova events. The first detection of a kilonova event was in 2013. A kilonova found in 2017 led to the detection of a gamma-ray burst, gravitational waves, and the production of heavy elements.