Evidence for orbital eccentricity supports a hierarchical origin for GW231123
Abstract
GW231123 is the most massive binary black hole merger observed to date and one of the most intriguing hierarchical merger candidates in the pair-instability mass gap. Its exceptionally large inferred component spins and remarkably short in-band duration make the source highly sensitive to waveform physics near merger. Here we show that GW231123 is better described as an eccentric binary black-hole merger. We analyse data over 11--448 Hz using the eccentric, spin-precessing effective-one-body waveform model TEOBResumS--Dalí, accounting for detector calibration uncertainty. We measure e5.5 Hz=0.34+0.12−0.23 at 90\% credibility and obtain a Bayes factor of 10.2 in favour of the eccentric model over its quasi-circular counterpart. GW231123-like injection--recovery studies further show that analyses starting at 20 Hz, as in previous studies, can obscure this eccentricity. Including eccentricity substantially changes the spin inference, weakening the preference for a near-extremal secondary spin and lowering its posterior median to a2≃0.7, close to the characteristic spin expected for a black-hole merger remnant. These results provide a coherent dynamical interpretation of GW231123, in which residual eccentricity, a mass-gap black hole, and a remnant-like spin arise naturally from a hierarchical merger channel in a dense environment.
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BibTeX
@misc{wang2026evidence,
title = {{Evidence for orbital eccentricity supports a hierarchical origin for GW231123}},
author = {Baoxiang Wang and Tao Yang and Zhoujian Cao and Bin Hu and Xikai Shan and Rong-Gen Cai},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.12205},
eprint = {2610.12205},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.12205},
}
RIS
TY - UNPB
TI - Evidence for orbital eccentricity supports a hierarchical origin for GW231123
AU - Baoxiang Wang
AU - Tao Yang
AU - Zhoujian Cao
AU - Bin Hu
AU - Xikai Shan
AU - Rong-Gen Cai
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2610.12205
UR - https://arxiv.org/abs/2610.12205
AB - GW231123 is the most massive binary black hole merger observed to date and one of the most intriguing hierarchical merger candidates in the pair-instability mass gap. Its exceptionally large inferred component spins and remarkably short in-band duration make the source highly sensitive to waveform physics near merger. Here we show that GW231123 is better described as an eccentric binary black-hole merger. We analyse data over 11--448 Hz using the eccentric, spin-precessing effective-one-body waveform model TEOBResumS--Dalí, accounting for detector calibration uncertainty. We measure e_5.5 Hz=0.34^+0.12_−0.23 at 90\% credibility and obtain a Bayes factor of 10.2 in favour of the eccentric model over its quasi-circular counterpart. GW231123-like injection--recovery studies further show that analyses starting at 20 Hz, as in previous studies, can obscure this eccentricity. Including eccentricity substantially changes the spin inference, weakening the preference for a near-extremal secondary spin and lowering its posterior median to a_2≃0.7, close to the characteristic spin expected for a black-hole merger remnant. These results provide a coherent dynamical interpretation of GW231123, in which residual eccentricity, a mass-gap black hole, and a remnant-like spin arise naturally from a hierarchical merger channel in a dense environment.
ER -