‘On a January morning in 2025, a ripple in the fabric of spacetime swept across the United States, arriving at two giant instruments a fraction of a second apart. Those instruments belong to the Laser Interferometer Gravitational-Wave Observatory (LIGO) — twin facilities in Washington State and Louisiana built specifically to catch these gravitational waves.

That signal, cataloged as GW250114, came from the merger of two near-equal black holes, about 34 and 32 times the mass of the Sun, and produced the clearest gravitational-wave signal yet recorded. The signal was about three times clearer than GW150914, the first gravitational wave ever directly detected in 2015.

A research team has now pulled a message out of that signal — one that had been hiding in plain sight for years. They describe the first direct measurements of two defining properties of a black hole’s event horizon…

“We measured the last sound the black holes made when they crashed. Hidden within that signal is a small component, called direct waves, that had not previously been well understood,” said Neil Lu, from the ANU Centre for Gravitational Astrophysics (CGA) and the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav). “Our new analysis allows us to decipher this component and extract unique information from close to the event horizon.”…’ (via ZME Science)