Kilonova r-process Nucleosynthesis

When two neutron stars merge, the neutron-rich matter they eject is bathed in such an intense neutron flux that atomic nuclei capture neutrons faster than they can beta-decay — the astrophysical rapid neutron-capture process, or r-process. This simulator runs the waiting-point approximation on a live chart of the nuclides: iron-group seed nuclei climb toward each proton number's neutron-capture equilibrium, stall at closed neutron shells (N = 50, 82, 126) where beta decay is dramatically slower, and pile up abundance there before the neutron supply runs out and freeze-out beta decay carries them down to stability. Watch the resulting abundance-vs-mass-number chart build the same three peaks — near A ≈ 80, 130 and 195 — that produced essentially all of the universe's gold, platinum and uranium, and that were confirmed observationally in the kilonova following GW170817.