In the GW250114 gravitational-wave event, astronomers have captured the first echoes from a black hole's event horizon—the invisible boundary from which nothing can return.
The signal was recorded in 2025 by LIGO detectors in Hanford and Livingston. After filtering out dominant quasinormal modes, researchers identified a residual component oscillating at nearly double the horizon's rotational frequency (Ω_H) and decaying at a rate set by surface gravity (κ). These parameters matched theoretical predictions for a Kerr black hole with high precision.
Theoretical work from 2025 had predicted this "direct wave," a gravitational-wave signal bearing the hallmarks of frame-dragging in the ergosphere and gravitational redshift near the horizon. In GW250114, this component's signal-to-noise ratio reached 15.8–17.1, enabling the properties of the resulting black hole to be measured directly.
This discovery provides the first observational pathway for investigating physics near the horizon within the dynamic regime of strong gravity. While such effects were once purely theoretical, they have now been confirmed in an actual black hole merger.
These findings were published in Nature on June 24, 2026, in the article "GW250114 reveals signatures of post-merger black-hole horizon."
