A kilonova is the glow produced when two neutron stars collide, powered by the radioactive decay of freshly forged heavy elements. The merger flings out neutron-rich debris in which the rapid neutron-capture process builds elements far beyond iron, including gold, platinum, and uranium. The first confirmed example, GW170817 in 2017, was detected in gravitational waves and then observed across the electromagnetic spectrum, tying these collisions to the origin of much of the heavy metal in the universe. Its brightness sits roughly a thousand times above a classical nova, which is where the name comes from.