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First overtone and higher-order modes in the ringdown signal of GW231028

Hai-Tian Wang (王海天)*

  • *Contact author: wanght9@dlut.edu.cn
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Phys. Rev. Research 8, 033065 – Published 16 July, 2026

DOI: https://doi.org/10.1103/114x-tj8m

Abstract

The properties of a remnant black hole can be probed by analyzing the gravitational waves emitted during its ringdown phase. This signal provides a direct test of general relativity in the strong-field regime. In this study, we apply both a time-domain F-statistic framework and full Bayesian time-domain sampling to the ringdown of GW231028_153006. We report decisive evidence for multimode content, specifically identifying both the first overtone (ℓ|m|n=221) and the higher order (ℓ|m|n=210). The detection of the 221 mode is statistically significant, achieving a Bayes factor of ∼189.2 and an amplitude exclusion from zero at >7σ credibility for an analysis beginning at 10M postpeak. These findings are rigorously validated against the numerical relativity injection SXS:BBH:1282, which confirms that such multimode features are physically expected for a remnant with the inferred high spin and mass ratio. The inclusion of the overtone mode allows for precise constraints on the remnant's properties, yielding a redshifted final mass of 246.2−22.4+22.3M⊙ and a final spin of 0.81−0.10+0.07 (at 90% credibility), consistent with full inspiral-merger-ringdown predictions. A test of the no-hair theorem, enabled by this robust multimode detection, shows consistency with general relativity.

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Phys. Rev. Research 8, 033065– Published 16 July, 2026
  • Received 14 September 2025
  • Accepted 18 June 2026
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