Hawking’s black hole theorem is confirmed by observation

There are some rules that even the most extreme objects in the universe must follow. A central law of black holes predicts that the area of a black hole’s event horizon (the boundary from which nothing can escape) will never shrink. This is the Hawking area theorem, named after physicist Stephen Hawking, derived by Hawking in 1971.
Fifty years later, a new study uses gravitational waves to produce evidence that the total area of a black hole’s event horizon never decreases. Physicists at MIT and elsewhere used observations of gravitational waves to confirm Hawking’s area theorem for the first time.
In the study, researchers took a closer look at GW150914, the first gravitational wave signal detected by the Stimulated Light Interference Gravitational-Wave Observatory (LIGO) in 2015. GW150914 is the product of two inner spinning black holes that merged to create a new black hole, releasing a lot of energy. This energy ripples through space-time in the form of gravitational waves.
If Hawking’s area theorem holds, the area of the new black hole’s event horizon should be no smaller than the total area of its two parent black holes. In the new study, physicists re-analyzed signals from GW150914 before and after the two black holes collided. They found that the total area of event horizons did not decrease after the merger — a result they reported with 95% confidence.
Their discovery marks the first direct observational confirmation of Hawking’s area theorem. Until now, Hawking’s area theorem had only been mathematically proven, but never observed in nature. The research team plans to test future gravitational wave signals in the hope of further confirming Hawking’s theorem or proving it is a sign of a new violation of the laws of physics.
Kraft astrophysics and space research institute at the Massachusetts institute of technology of NASA Einstein postdoctoral researcher, the study’s lead author horse sago leah northrop grumman izzy, said: “there may be a different density of objects’ zoo ‘, although some of the black hole follow the laws of Albert Einstein and Stephen Hawking, but others may be slightly different beast. So, it’s not like doing one of these tests is done. This test is just the beginning.”
The age of Insight
In 1971, Stephen Hawking formulated the area theorem, which led to a series of fundamental insights into the mechanics of black holes. The area theorem predicts that the total area of black hole event horizons — and all black holes in the universe — will never decrease. This statement is eerily similar to the second law of thermodynamics, which states that entropy, or the degree of disorder inside objects, can never decrease either.
The similarity between the two theorems suggests that black holes may behave as hot, heat-emitting objects — a puzzling claim since, by their very nature, black holes are thought never to allow energy to escape or radiate. Hawking finally explained both ideas in 1974, suggesting that black holes could have entropy and emit radiation on extremely long time scales if their quantum effects were taken into account. This phenomenon is known as hawking radiation and remains one of the most fundamental Revelations about black holes.
“It all started with Hawking’s realization that the total event horizon area of a black hole never decreases,” Issey said. The area theorem encapsulates a golden age in the seventies, from which all these insights come.”
Hawking and others have shown that the area theorem works mathematically, but until LIGO first detected gravitational waves, there was no way to verify the theorem with natural observations.
When Hawking heard that LIGO had detected gravitational waves, he immediately contacted Its co-founder, Kip Thorne, a professor of theoretical Feynman physics at The California Institute of Technology. Hawking raised his own question: Could LIGO’s findings confirm the area theorem?
At the time, however, researchers were not able to build confidence from the gravitational wave signals before and after the black hole merger to determine whether the final event horizon area had not decreased, as Hawking’s area theorem predicted. A few years later, Issy and his colleagues developed a technique that made it possible to test the area theorem.
Before and after
In 2019, Issy and his colleagues developed a technique that could extract the reverberation of GW150914 moments after its peak. This is the moment when the two parent black holes merge to form a new black hole. The team then used the technique to pick out tones of specific frequencies, or other noisy consequences, which they could use to calculate the mass and spin of the resulting black hole.
The mass and spin of a black hole are directly related to the area of its event horizon. Thorne recalled Hawking’s question and asked the team a follow-up question: Could they use the same technique to compare confidence before and after black hole mergers and confirm the area theorem?
The researchers took up the challenge and split the GW150914 signal again at the peak. They developed a model to analyse the signal before the peak, corresponding to two inner-spinning black holes, and confirm their respective mass and spin before merging. From these estimates, they calculated that the total event horizon of the two black holes was about 235,000 square kilometers, or nine times the size of Massachusetts.
They then used previous techniques to extract the “closing bell,” or reverberation, of the newly formed black hole to calculate the mass and spin of the new black hole and, finally, the area of the event horizon. They found that the event horizon of the new black hole is about 367,000 square kilometers, or 13 times the size of Massachusetts.
“The data show that the combined event horizon area is unquestionably increased, and the probability of satisfying the area theorem is high in ten,” Issey said. This is very reassuring, our results are consistent with the paradigm we expected and really confirm our understanding of these complex black hole mergers.”
The team plans to further test Hawking’s area theorem and other long-standing black hole mechanics theories in the future, using data from LIGO and Virgo, an interferometer based near Pisa, Italy, that detects gravitational waves.
Issey said: “It’s encouraging that we can think about gravitational wave data in new and creative ways and answer questions we previously thought were unanswerable. We can constantly tease out information that is directly relevant to what we think are the pillars of understanding. One day, this data may reveal something we didn’t expect.”