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arXiv · 2511.06536

Constraining Black Hole Horizon Properties Through Long-Duration Gravitational Wave Observations

Ikram Hamoudy·Julian Westerweck·Ofek Birnholtz
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Abstract

We perform a long-duration Bayesian analysis of gravitational-wave data to constrain the near-horizon geometry of black holes formed in binary mergers. Deviations from the Kerr geometry are parameterized by replacing the horizon's absorbing boundary with a reflective surface at a fractional distance epsilon. This modification produces long-lived monochromatic quasinormal modes that can be probed through extended integration times. Building on previous work that set a bound of log10(epsilon) = -24 for GW150914, we reproduce and validate those results and extend the analysis to additional events from the LIGO-Virgo-KAGRA observing runs. By combining posterior samples from multiple detections, we construct a joint posterior yielding a tightened 90 percent upper bound of log10(epsilon) < -38.64, demonstrating the statistical power of population-level inference through cumulative evidence. Finally, analyzing the newly observed high signal-to-noise ratio event GW250114 from the O4b run, we obtain the most stringent single-event constraint to date, log10(epsilon) < -29.58 (90 percent credible region). Our findings provide the strongest observational support to date for the Kerr geometry as the correct description of post-merger black holes, with no detectable horizon-scale deviations.

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Ikram Hamoudy, Julian Westerweck, Ofek Birnholtz. 2025-11-09. Constraining Black Hole Horizon Properties Through Long-Duration Gravitational Wave Observations. https://arxiv.org/abs/2511.06536

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