In his theory, Hawking assumed that the total event horizon of any group of black holes would never shrink.
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Scientists led by experts from the Massachusetts Institute of Technology (MIT) in Cambridge, USA, analyzed two black holes that merged to form a larger black hole, along with huge amounts of energy that rippled across space-time like gravitational waves. Hawking’s theorem on the area of black holes was first confirmed by observing gravitational waves, the Daily Mail reported.
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| Black holes they are very material objects that have such strong gravity that no object, including light or other radiation, can leave them. The escape velocity from a black hole is higher than the speed of light. According to the theory of relativity, there is nothing faster than light, so nothing can leave this boundary. Therefore, it is not possible to obtain information about the mass in the black hole. |
| The black hole is made of black by the so-called event horizon, which is a kind of border of a black hole and a place around it from which it is no longer possible to get out or send any signal out. |
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Physicists from MIT and other scientific institutions analyzed the impact of a collision or fusion of two black holes observed by gravitational waves. It was an event called GW150914 – the very first detected signal of gravitational waves, which was detected in 2015 by the American observatory LIGO.
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Both black holes first had an area of about 235 thousand square kilometers, after a collision of 367 thousand square kilometers.
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The signal from GW150914, using computer simulation, was investigated before and after the cosmic collision of black holes in terms of the validity of Hawking’s theorem. The researchers found, with 95 percent confidence, that the total area of the event horizon did not actually decrease after the holes merged.
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“On the contrary, the new calculations showed that the total event horizon area of the two connected black holes was greater than the sum of the two smaller holes,” according to a recent study by Physical Review Letters.
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The concrete result was as follows: both black holes initially had an area of about 235 thousand square kilometers, after a collision of 367 thousand square kilometers, according to the MIT website.
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Help from Einstein
Hawking derived his 50-year-old hypothesis from Albert Einstein’s theory of relativity, which predicted the existence of gravitational waves and black holes. The current confirmation of Hawking’s theorem thus further strengthens the position of Einstein’s theory.
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The freshly obtained data confirm that the size of black holes does not decrease over time, so certainly not for all. Thus, with all changes in black holes, the area of the event horizon should increase or at least not decrease – analogously to the increase in entropy (the degree of disorder of the system), says the scientific team.
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This was previously clear to scientists when a “normal” object fell into a black hole (the black hole enlarges, including the area of the horizon), but less clear in the case of the fusion of two black holes, when two areas add up.
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Hawking was very interested
It is also worth noting that when Hawking (who died on March 14, 2018) learned of the recording of the black hole fusion, he contacted LIGO co-founder Kip Thorn of the California Institute of Technology. He wanted to know if his theorem on the surface of the horizon could be confirmed from the detected gravitational waves. However, this technology has not yet been available that would allow the data to be obtained from the gravitational wave signal.
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In 2019, however, Maximiliano Isi from MIT came with her, who is also the main author of the newly published study. His technique made it possible to extract from the signal the “reverberations” that follow the maximum of the signal – the collision itself. From them it was possible to calculate the mass and spin (momentum) of the resulting black hole, from the mass also the area of the event horizon.
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The physicist Thorne then suggested, referring to Hawking, that the signal before the peak, which corresponded to the original two black holes, be similarly analyzed.
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According to scientists, this is not an “irreversible and universally valid confirmation” of Hawking’s theorem, as black holes and their fusions can be of various types, but rebuttal is not expected in the professional community.
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