Two neutron stars whirl in their final dance. If their spin aligns with their orbital motion, the partners merge neatly, launching a narrow jet of superheated matter. If they spin in opposite directions, the dance breaks apart, scattering a thick shroud of debris.
In cleaner mergers, ghostly neutrinos convert the ejecta into proton-rich material. There, nickel-56 is born: a radioactive element that, as it decays, glows for weeks, almost like a mini-supernova. Although this flash is too slow for a typical gamma-ray burst, using spectroscopy (the splitting of light) scientists can detect the presence of heavy elements. But the real surprise: in this chaos, the heaviest elements on the periodic table, from platinum to uranium, are forged.
In a few seconds, such a merger produces more gold than humans have mined in all of history.
In Peter Hamilton’s novel *The Neutronium Alchemist*, neutron star matter is the raw material for fantastic elements. Nature truly practices alchemy: in these mergers, the r-process forges gold and uranium.