In 2017, detectors on two continents felt a tremor in space-time: the first observed neutron star merger, GW170817. Seconds later, telescopes caught the glow of a kilonova — the radioactive fireball where some of the universe's heaviest elements are made.

A neutron star packs more mass than the Sun into a sphere the size of a city. When two of them spiral together, the final collision ejects neutron-rich material at a tenth of the speed of light.

The r-process

In that ejecta, atomic nuclei capture neutrons faster than they can decay — the rapid neutron-capture process, or r-process. This is how nature builds gold, platinum, and uranium. A single neutron star merger can produce several Earth-masses of gold.

Multi-messenger astronomy

GW170817 marked the beginning of multi-messenger astronomy: the same event observed in gravitational waves, gamma rays, visible light, and radio. Each messenger tells a different part of the story, from the physics of ultra-dense matter to the expansion rate of the universe.

Future detector upgrades should let us catch dozens of these events every year, turning cosmic gold factories into routine science.