Rapid neutron capture in neutron star mergers — forging heavy elements
The r-process (rapid neutron capture) occurs when neutron flux is so intense that neutron captures proceed faster than beta decay. Each nucleus captures neutrons until reaching the drip line, then beta-decays toward stability. GW170817 confirmed neutron star mergers as r-process sites via kilonova observation. Half of all elements heavier than iron, including gold and platinum, formed this way.