The merger wasn’t just the biggest ever, but also an event so rare that it challenges existing models for black hole genesis.

Gravitational-wave detectors have captured their biggest spectacle yet: two gargantuan, rapidly spinning black holes likely forged by earlier smash-ups fused into a 225-solar-mass titan, GW231123. The record-setting blast strains both the sensitivity of LIGO-Virgo-KAGRA and the boundaries of stellar-evolution theory,