Hawking was right: New data confirms black holes never shrink

New observations of two merging black holes confirm Stephen Hawking's predictions based on Einstein's theory

A decade after the first detection of gravitational waves from two merging black holes, the LIGO-Virgo-KAGRA collaboration, including astronomer Maximiliano Izzi, has picked up another signal from a nearly identical cosmic event.

Thanks to important developments in the sensitivity of the detectors, the team observed the collision with almost four times greater clarity than before, which allowed them to verify two long-standing theoretical predictions: black holes formed in mergers never shrink, according to Stephen Hawking's theory, and they "ring" after the merger, as predicted by Einstein's general theory of relativity.

"This unprecedentedly clear signal of a black hole merger, known as GW250114, challenges some of the most important hypotheses about black holes and gravitational waves," Izzi said.

Testing Hawking's black hole area theorem

In 1971, Hawking proposed that the event horizon of a black hole – the outer boundary beyond which nothing, not even light, can escape – can never shrink.

In 2021, Izzi and his colleagues used data from the LIGO Gravitational-Wave Observatory to detect high-energy ripples in space-time created by colliding black holes, providing the first observational confirmation of Hawking's prediction. At the time, The New York Times noted that if the result had been published while Hawking was still alive, it might have earned him a Nobel Prize.

The new findings reinforce the previous conclusion with much greater precision, confirming that the surface area of ​​the resulting black hole is always at least as large as the combined areas of the two that merged. The improved precision was achieved using data from the two LIGO observatories, in Washington state and Louisiana.

Listen to the "ringing" of black holes

The researchers were also able to isolate and analyze the gravitational waves emitted by the black holes after they merged. By measuring the height and duration of the waves, they were able to learn more details about the structure and properties of the merged black hole. (The process works much like analyzing the pitch of a hollow instrument to determine the size and shape of the instrument and the object that hit it.)

The researchers confirmed that the merged black hole fits what is known as a “Kerr-type black hole.” Mathematician Roy Kerr, who worked in the 1960s, solved Einstein’s space-time equations, and presented a detailed mathematical solution of what the gravity, space, and time of a black hole should be like.

Physicists believe Kerr's solution must describe all black holes, but verifying it is a known challenge. By studying the vibrations of the finite black hole in this unusually clear signal, Izzy and the LIGO collaboration have obtained the most direct evidence yet that black holes behave as Kerr predicted.

for the scientific article

More of the topic in Hayadan:

• The quantum mechanics of black holes
• LIGO Detects Gravitational Waves from Extreme Black Hole Merger *Pushing the Limits of Einstein's Theory of Relativity
• Thousands of people came to the Hebrew University to hear Prof. Stephen Hawking's lecture on the origin of the universe
• Researchers in Tel Aviv shed light on the period when the black holes grew
• Hawking: Time travel is possible but only into the future