Gravitational wave GW250114 has revealed signatures of the “post-merger” phase of a black hole immediately after merging, a phase previously difficult to observe. Researchers led by Neil Lu of OzGrav-ANU, in collaboration with Sizheng Ma at the Perimeter Institute for Theoretical Physics, detected a component within the signal oscillating near twice the black hole horizon’s rotation frequency. The team reports a matched-filter signal-to-noise ratio of 15.8 – 0.5 + 0.1 (17.1 – 0.4 + 0.1) in the LIGO Hanford detector, confirming properties consistent with a Kerr black hole. These findings establish a new observational channel to directly measure frame-dragging effects and explore the extreme physics occurring near black hole horizons, as predicted by recent theoretical work.
GW250114 Reveals Post-Merger Black-Hole Horizon Signatures
GW250114 has provided the first direct observation of a “direct wave” emanating from the immediate aftermath of a black hole merger, a signal predicted by theoretical work to carry imprints of the newly formed black hole’s horizon properties. This discovery moves beyond simply detecting the merger event itself, offering a glimpse into the previously murky post-merger phase and allowing scientists to probe the extreme gravity near the black hole’s event horizon. A signal-to-noise ratio of 15.8 – 0.5 + 0.1 (17.1 – 0.4 + 0.1) was detected in the LIGO Hanford detector, indicating a robust detection of this subtle signal. Neil Lu of OzGrav-ANU, Centre for Gravitational Astrophysics at The Australian National University, is a lead author on the research, highlighting the significant contribution of Australian scientists to this international effort.
According to recent theoretical work, the observed “direct wave” oscillates near 2ΩH, reflecting the frame-dragging effect of the black hole’s horizon, while decaying at a rate determined by the surface gravity, κ. Sizheng Ma of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, is a co-author, demonstrating the collaborative nature of this research spanning multiple continents. The researchers found that the measured properties are in full agreement with theoretical predictions for a Kerr black hole, a rotating black hole described by a specific mathematical solution.
Here we report observational evidence of a direct wave in GW250114 2 , with a 90% credible matched-filter signal-to-noise ratio of 15.8 – 0.5 + 0.1 ( 17.1 – 0.4 + 0.1 ) in the LIGO Hanford (Livingston) detector.
This detection moves beyond simply identifying mergers to probing the spacetime immediately following them, a previously murky phase in black hole evolution. The signal-to-noise ratio was 15.8 – 0.5 + 0.1 (17.1 – 0.4 + 0.1). This direct wave carries imprints of the remnant black hole’s properties, specifically its surface gravity and rotation, offering a new way to test Einstein’s theory of general relativity in extreme conditions.
