What it is
On 23 November 2023 the two LIGO observatories both detected GW231123, a gravitational-wave signal consistent with the merger of two black holes of 137 (+23/−18) and 101 (+22/−50) solar masses (90% credible intervals), at a luminosity distance of 0.7 to 4.1 Gpc and a redshift of 0.40, with a network signal-to-noise ratio of about 20.7. Both black holes have high spins, 0.90 and 0.80 respectively, and an independent ringdown analysis supports a massive remnant black hole. Some properties of GW231123 are subject to large systematic uncertainties, as differences between the parameters inferred with different signal models show. The primary black hole lies within or above the theorized mass gap where black holes between 60 and 130 solar masses should be rare because of pair-instability mechanisms, while the secondary spans the gap. The authors conclude that GW231123 suggests black holes form through channels beyond standard stellar collapse, and that intermediate-mass black holes of about 200 solar masses form through gravitational-wave-driven mergers.
Why it matters
With a total mass of 190 to 265 solar masses, GW231123 is the highest-mass black hole binary the LIGO-Virgo-KAGRA collaboration has observed to date. The paper ranks it so among signals passing a false-alarm-rate threshold of 1 per year. Its primary black hole lies within or above the pair-instability mass gap and its secondary spans it, so the authors read the event as suggesting that black holes also form through channels beyond standard stellar collapse, with black holes of about 200 solar masses built up through mergers; the full text puts the remnant at 222 (+28/−42) solar masses.
Underlined numbers link to their source. Every metric and quoted figure is listed under Sources and data below.
Filed undergravitational waves, black holes, LIGO, astrophysics, mass gap
