A massive star appears to have exploded twice — first as a supernova, and then again days later when the two neutron stars its first explosion had created violently crashed into each other — in what astronomers announced in December 2025 may be the first event of its kind ever observed, so unprecedented that physicists have invented a new word for it: "superkilonova"

A massive star appears to have exploded twice — first as a supernova, and then again days later when the two neutron stars its first explosion had created violently crashed into each other — in what astronomers announced in December 2025 may be the first event of its kind ever observed, so unprecedented that physicists have invented a new word for it: "superkilonova"

The unusual sequence began with a signal from a routine source. On 18 August 2025, the LIGO gravitational wave detectors in the United States and the Virgo detector in Italy registered ripples in spacetime characteristic of two compact objects merging — the kind of signal that has, since 2017, become the standard signature of binary neutron star mergers. The follow-up alert went out to the global astronomical community within minutes. Optical te…