General-relativistic precession in a black-hole binary

The general-relativistic phenomenon of spin-induced orbital precession has not yet been observed in strong-field gravity. Gravitational-wave observations of binary black holes (BBHs) are prime candidates, as we expect the astrophysical binary population to contain precessing binaries 1 , 2 . Imprints of precession have been investigated in several signals 3 – 5 , but no definitive identification of orbital precession has been reported in any of the 84 BBH observations so far 5 – 7 by the Advanced LIGO and Virgo detectors 8 , 9 . Here we report the measurement of strong-field precession in the LIGO–Virgo–Kagra gravitational-wave signal GW200129. The binary’s orbit precesses at a rate ten orders of magnitude faster than previous weak-field measurements from binary pulsars 10 – 13 . We also find that the primary black hole is probably highly spinning. According to current binary population estimates, a GW200129-like signal is extremely unlikely, and therefore presents a direct challenge to many current binary-formation models. Analysis of a gravitational-wave signal reveals a strongly precessing black-hole binary that contains a rapidly spinning black hole.