GW250114 reveals signatures of post-merger black-hole horizon.
basic_science · Level V
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- Record sourced from PubMed, PMID 42343129.
- Also identified by DOI 10.1038/s41586-026-10696-0.
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Abstract
The horizon of a black hole, the 'surface of no return', is characterized by its rotation frequency Ω<sub>H</sub> and surface gravity κ. A striking signature is that any infalling object appears to orbit at Ω<sub>H</sub> owing to frame dragging, while its emitted signals decay exponentially at a rate set by κ as a consequence of gravitational redshift. Recent theoretical work<sup>1</sup> predicts that gravitational waves from binary black-hole mergers carry direct imprints of the properties of the merger remnant in the form of a 'direct wave'. This gravitational-wave component oscillates near 2Ω<sub>H</sub>, reflecting the horizon's frame dragging, and decays at an increasing rate characterized by κ, with additional screening from the black hole's spacetime. Here we report observational evidence of a direct wave in GW250114<sup>2</sup>, with a 90% credible matched-filter signal-to-noise ratio of <math xmlns="http://www.w3.org/1998/Math/MathML"> <msubsup><mrow><mn>15.8</mn></mrow> <mrow><mo>-</mo> <mn>0.5</mn></mrow> <mrow><mo>+</mo> <mn>0.1</mn></mrow> </msubsup> </math> ( <math xmlns="http://www.w3.org/1998/Math/MathML"> <msubsup><mrow><mn>17.1</mn></mrow> <mrow><mo>-</mo> <mn>0.4</mn></mrow> <mrow><mo>+</mo> <mn>0.1</mn></mrow> </msubsup> </math> ) in the LIGO Hanford (Livingston) detector. The measured properties are in full agreement with theoretical predictions for a Kerr black hole. These findings establish an observational channel to directly measure frame-dragging effects in black-hole ergospheres and explore (near-)horizon physics in dynamical, strong-gravity regimes.