GW250114 reveals black hole horizon signatures

The horizon of a black hole, the "surface of no return," is characterized by its rotation frequency ΩH and surface gravity $κ$. A striking signature is that any infalling object appears to orbit at ΩH due to frame dragging, while its emitted signals decay exponentially at a rate set by $κ$ as a consequence of gravitational redshift. Recent theoretical work predicts that the merger phase of gravitational waves from binary black hole coalescences carries direct imprints of the remnant horizon's properties, via a "direct wave" component that (i) oscillates near 2ΩH, reflecting the horizon's frame dragging and the quadrupole nature of the gravitational radiation, and (ii) decays at an increasing rate characterized by $κ$, with additional screening from the black hole's potential barrier. In this paper, we report observational evidence for the direct wave in GW250114 with a matched-filter signal-to-noise ratio of 14.0+0.2-0.1 (13.5+0.1-0.2) in the LIGO Hanford (Livingston) detector. The measured properties are in full agreement with theoretical predictions. These findings establish a new observational channel to directly measure frame-dragging effects in black hole ergospheres and explore (near-)horizon physics in dynamical, strong-gravity regimes.