Two black holes just rang like a cosmic bell — and proved Einstein and Hawking right

Astronomers have caught a black-hole smash-up in astonishing detail, turning a once-theoretical thought experiment into a lab-grade test of gravity — and it passed with flying colors for both Albert Einstein and Stephen Hawking.

The event, tagged GW250114, was picked up by the LIGO detectors in Louisiana and Washington state, with backup from sister observatories Virgo (Italy) and KAGRA (Japan). What LIGO “heard” were gravitational waves: faint ripples in spacetime predicted by Einstein in 1915 and first detected in 2015. This time, the signal was so clean it let scientists dissect the final “ring” of the newly formed black hole, confirming two famous predictions about how these extreme objects behave.

In GW250114, two black holes each about 30–35 times the Sun’s mass spiraled together roughly a billion light-years away. They were “orbiting around each other in almost a perfect circle,” said Maximiliano Isi of Columbia University and the Flatiron Institute, who led the analysis for the LIGO–Virgo–KAGRA Collaboration. When they merged, they formed a remnant about 63 solar masses, spinning roughly 100 times per second.

If that sounds familiar, it’s because it’s almost a carbon copy of LIGO’s historic 2015 detection — only now the detectors’ upgraded lasers and mirrors have slashed the noise. The result: a measurement more than three times sharper than a decade ago, offering a front-row seat to the final, vibrating “ringdown” of the merged black hole.

Think of the newborn black hole as a struck bell. The pitch and fade of its ringing — carried to us as gravitational waves — are determined by what the object is made of. For black holes, theory says that’s shockingly simple.

Back in 1963, mathematician Roy Kerr found that black holes in Einstein’s theory should be featureless: fully described by just two numbers, mass and spin (astrophysical black holes carry no net electric charge). This idea is often nicknamed the “no-hair” property.

GW250114 delivered the clearest ring we’ve heard yet — and crucially, it revealed two distinct tones of the ringdown: the fundamental mode and a fainter overtone.

“We identified two components of this ringing, and that allowed us to test that this black hole really is consistent with being described by just two numbers,” Isi said.

In other words: the data match Kerr’s prediction. No extra “hair” required.

The signal also nailed a second classic result: Stephen Hawking’s surface-area theorem from 1971. It sounds simple but it’s deep: the total surface area of black holes can never decrease. When two holes merge, the area of the final horizon must be at least as large as the sum of the originals.

Earlier LIGO events hinted at this; GW250114 makes it convincing. By teasing apart the early inspiral (when the two holes are still separate) from the late ringdown (after merger), the team inferred the before-and-after areas — and the area went up, just as Hawking said. Nobel laureate Kip Thorne noted Hawking had asked back in 2015 whether LIGO could ever test his theorem. If he were here, Thorne said, “he would have reveled in seeing the area of the merged black holes increase.”

“We can now test fundamental principles of gravity that we could not test ten years ago,” said Emanuele Berti of Johns Hopkins, who wasn’t involved.

The result strengthens the case that astrophysical black holes are the Kerr black holes of general relativity.

LIGO and partners have now logged 300+ mergers, including the most massive yet (about 100 and 140 solar masses). As the detectors keep improving, multi-tone “ringdowns” like GW250114 will become the gold standard for stress-testing Einstein’s equations.

Nailing Hawking’s area law — rooted in Einstein’s framework — feeds into the longer game: reconciling general relativity with quantum mechanics. Clean, high-fidelity ringdowns are among the best arenas for spotting any tiny cracks.

Einstein once suspected gravitational waves might be too weak for humans to ever detect. Not only are we detecting them, we’re now using them like a stethoscope on spacetime, confirming that black holes really do behave like the elegant, minimal objects theorists drew on chalkboards decades ago. As Leor Barack (University of Southampton) put it, GW250114’s clear extraction of a first overtone makes this “the most precise test to date, by a long margin.”

Or, as Isi summed up:

“This gives us a totally new view into the dynamics of space and time.”

The universe rang; we listened — and two of physics’ boldest ideas came through loud and clear.

The original story by Jacopo Prisco for CNN.