GW231123: A Binary Black Hole Merger with Total Mass 190–265 M ⊙
Adrian Abac, I. Abouelfettouh, F. Acernese, K. Ackley, Christian Adamcewicz, S. Adhicary et al. · 2025 · 128 citationsRead the paper
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 13 7 − 18 + 23 M ⊙ and 10 1 − 50 + 22 M ⊙ (90% credible intervals), at a luminosity distance of 0.7–4.1 Gpc, a redshift of 0.4 0 − 0.25 + 0.27 , and with a network signal-to-noise ratio of ∼20.7. Both black holes exhibit high spins— 0.9 0 − 0.19 + 0.10 and 0.8 0 − 0.52 + 0.20 , 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 the inferred parameters between signal models. The primary black hole lies within or above the theorized mass gap where black holes between 60–130 M ⊙ 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 ∼200 M ⊙ form through gravitational-wave-driven mergers.
What the full text shows
Tested in real conditions- Detection of a binary black hole merger with a total mass between 190 and 265 M⊙. — 190–265 M⊙ (LIGO Hanford and Livingston detectors)
- Primary black hole mass inferred with a 90% credible interval. — 137 +23 −18 M⊙ (LIGO Hanford and Livingston detectors)
- Secondary black hole mass inferred with a 90% credible interval. — 101 +22 −50 M⊙ (LIGO Hanford and Livingston detectors)
- High spins detected for both black holes. — 0.90 +0.10 −0.19 and 0.80 +0.20 −0.52 (LIGO Hanford and Livingston detectors)
- Network signal-to-noise ratio (SNR) of the event. — ~20.7 (LIGO Hanford and Livingston detectors)
- Luminosity distance and redshift of the source. — 0.7–4.1 Gpc; redshift 0.40 +0.27 −0.25 (LIGO Hanford and Livingston detectors)
- Setup
- Data from LIGO Hanford and LIGO Livingston detectors; 8 seconds of data (20–448 Hz range); 1000 to 3000 live points for sampling.
- How
- Coherent Bayesian analysis of LIGO data using five IMR signal models (NRSur7dq4, SEOBNRv5PHM, IMRPhenomTPHM, IMRPhenomXPHM, and IMRPhenomXO4a) and nested sampling via the bilby library. An independent ringdown analysis was performed to support the black hole remnant interpretation.
- Limitations
- Large systematic uncertainties due to disagreement between different waveform models. · Lack of numerical-relativity calibrated models for precessing binaries with spins above 0.8. · Short signal duration (~0.1 s) and limited bandwidth (30–80 Hz).
Summarized by Gemma 4 from the open-access full text · 11 Oct 2026. Read it