![]() ![]() It wasn’t until several years later, and the development of a technique by Isi and his colleagues, when testing the area law became feasible. His question: Could the detection confirm the area theorem?Īt the time, researchers did not have the ability to pick out the necessary information within the signal, before and after the merger, to determine whether the final horizon area did not decrease, as Hawking’s theorem would assume. Hawking, on hearing of the result, quickly contacted LIGO co-founder Kip Thorne, the Feynman Professor of Theoretical Physics at Caltech. Hawking and others have since shown that the area theorem works out mathematically, but there had been no way to check it against nature until LIGO’s first detection of gravitational waves. “The area law encapsulates a golden age in the ’70s where all these insights were being produced.” “It all started with Hawking’s realization that the total horizon area in black holes can never go down,” Isi says. This phenomenon was dubbed “Hawking radiation” and remains one of the most fundamental revelations about black holes. Hawking eventually squared the two ideas in 1974, showing that black holes could have entropy and emit radiation over very long timescales if their quantum effects were taken into account. ![]() ![]() The similarity between the two theories suggested that black holes could behave as thermal, heat-emitting objects - a confounding proposition, as black holes by their very nature were thought to never let energy escape, or radiate. The statement was a curious parallel of the second law of thermodynamics, which states that the entropy, or degree of disorder within an object, should also never decrease. The theorem predicts that the total area of a black hole’s event horizon - and all black holes in the universe, for that matter - should never decrease. In 1971, Stephen Hawking proposed the area theorem, which set off a series of fundamental insights about black hole mechanics. Isi’s co-authors on the paper are Will Farr of Stony Brook University and the Flatiron Institute’s Center for Computational Astrophysics, Matthew Giesler of Cornell University, Mark Scheel of Caltech, and Saul Teukolsky of Cornell University and Caltech. You do this once, and it’s the beginning.” “So, it’s not like you do this test once and it’s over. “It is possible that there’s a zoo of different compact objects, and while some of them are the black holes that follow Einstein and Hawking’s laws, others may be slightly different beasts,” says lead author Maximiliano Isi, a NASA Einstein Postdoctoral Fellow in MIT’s Kavli Institute for Astrophysics and Space Research. ![]() The team plans to test future gravitational-wave signals to see if they might further confirm Hawking’s theorem or be a sign of new, law-bending physics. Their findings mark the first direct observational confirmation of Hawking’s area theorem, which has been proven mathematically but never observed in nature until now. In the new study, the physicists reanalyzed the signal from GW150914 before and after the cosmic collision and found that indeed, the total event horizon area did not decrease after the merger - a result that they report with 95 percent confidence. If Hawking’s area theorem holds, then the horizon area of the new black hole should not be smaller than the total horizon area of its parent black holes. The signal was a product of two inspiraling black holes that generated a new black hole, along with a huge amount of energy that rippled across space-time as gravitational waves. In the study, the researchers take a closer look at GW150914, the first gravitational wave signal detected by the Laser Interferometer Gravitational-wave Observatory (LIGO), in 2015. Their results appear today in Physical Review Letters. This law is Hawking’s area theorem, named after physicist Stephen Hawking, who derived the theorem in 1971.įifty years later, physicists at MIT and elsewhere have now confirmed Hawking’s area theorem for the first time, using observations of gravitational waves. A central law for black holes predicts that the area of their event horizons - the boundary beyond which nothing can ever escape - should never shrink. There are certain rules that even the most extreme objects in the universe must obey. ![]()
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