Neutron Star Mergers

When two neutron stars spiral together and collide, they produce a kilonova — an explosion that forges enormous quantities of heavy elements. The 2017 detection of gravitational waves from merger GW170817, combined with electromagnetic observations, confirmed that kilonovae produce heavy elements such as gold and platinum.

That single event forged an estimated 200 Earth-masses of gold — along with even more platinum — and scattered this material into the surrounding space. Over billions of years, it mixes with interstellar gas and gets incorporated into new stars and planets.