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

Astrophysicists have analyzed two merging black holes; the team's best models suggest that at least one, if not both, of the black holes shouldn't exist.

What occurs when the universe plays a cosmic curveball, breaking down long-standing assumptions about how black holes form? On 23 November 2023, the LIGO-Virgo-KAGRA Collaboration observed a gravitational wave signal GW231123 that would become an instant classic in the field of astrophysics.