GW231123: a Binary Black Hole Merger with Total Mass 190-265 $M_{\odot}$

TL;DR

GW231123 is a gravitational-wave detection of a binary black hole merger with total mass between 190 and 265 solar masses, indicating possible formation of intermediate-mass black holes through mergers.

Contribution

This paper reports the first detection of a binary black hole merger with a total mass in the pair-instability mass gap, suggesting new formation channels for intermediate-mass black holes.

Findings

Black holes with masses 137 and 101 solar masses detected.

Primary black hole within or above the pair-instability mass gap.

Evidence supports formation of intermediate-mass black holes via mergers.

Abstract

On 2023 November 23 the two LIGO observatories both detected GW231123, a gravitational-wave signal consistent with the merger of two black holes with masses $137^{+23}_{-18}\, M_\odot$ and $101^{+22}_{-50}\, M_\odot$ (90\% credible intervals), at luminosity distance 0.7-4.1 Gpc and redshift of $0.40^{+0.27}_{-0.25}$, and a network signal-to-noise ratio of $\sim$20.7. Both black holes exhibit high spins, $0.9^{+0.10}_{-0.19}$ and $0.80^{+0.20}_{-0.52}$ respectively. A massive black hole remnant is supported by an independent ringdown analysis. Some properties of GW231123 are subject to large systematic uncertainties, as indicated by differences in inferred parameters between signal models. The primary black hole lies within or above the theorized mass gap where black holes between 60-130 $M_\odot$ should be rare due to pair instability mechanisms, while the secondary spans the gap. The observation of GW231123 therefore suggests the formation of black holes from channels beyond standard stellar collapse, and that intermediate-mass black holes of mass $\sim$200 $M_\odot$ form through gravitational-wave driven mergers.