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

TL;DR

This paper uses long-duration gravitational wave data analysis to place stringent constraints on deviations from the Kerr black hole geometry, supporting the classical black hole model with no detectable horizon-scale deviations.

Contribution

It extends previous bounds on horizon deviations by analyzing multiple events and combining data, achieving the tightest constraints to date on black hole near-horizon geometry.

Findings

No detectable deviations from Kerr geometry in observed black holes.

Combined data yields a 90% upper bound of log10(epsilon) < -38.64.

Single-event analysis of GW250114 sets the most stringent constraint to date.

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.