The area of a black hole is related to the degree of disorder in the universe.

Wednesday, 23rd June 2021

Despite its mysterious nature, people believe that black holes follow certain simple rules. Now, one of the most famous black hole laws predicted by the physicist Stephen Hawking has been confirmed by gravitational waves. According to the black hole area theorem proposed by Hawking in the early 1970s, the surface area of ??a black hole will not decrease over time. The area theorem fascinates physicists because it reflects a well-known physical rule that disorder or entropy does not decrease over time. On the contrary, entropy is constantly increasing. Will Farr, an astrophysicist at Stony Brook University in New York and the Flatiron Institute in New York City, said this is "an exciting clue that the area of ??a black hole is a basic and important thing."

The surface area of ??a single black hole will not change; after all, nothing can escape him. However, if you throw something into a black hole, it will gain more mass and increase its surface area. But incoming objects can also rotate the black hole, thus reducing the surface area. The area law states that the increase in surface area due to increased mass is always greater than the decrease in surface area due to increased spin. To test this area law, MIT astrophysicists Maximiliano Issi, Farr, and others used spacetime waves, two black holes that spin inward and merge into a larger black hole.

The surface area of ??a black hole is defined by its event horizon; it is an impossible limit. By the area theorem, the area of ??the event horizon of the newly formed black hole should be at least as large as the sum of the areas of the event horizon of the two original black holes. The team analyzed data from the first gravitational wave ever discovered, which was detected by the LIGO Advanced Laser Interferometer Gravitational-Wave Observatory in 2015. The researchers divided the gravitational wave data into two time periods before and after the merger and calculated the surface area of ??the black hole in each period.

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The surface area of ??the newly formed black hole is greater than the sum of the surface areas of the two initial black holes, maintaining the area law with 95% confidence, the team reported in a paper to be published in Physical Review Letters. "This is the first time we can add a number to this number," Isi said.

The area theorem is the result of general relativity, which describes the physics of black holes and gravitational waves. The previous analysis of gravitational waves is consistent with the predictions of general relativity, so it has been implied that the law of area cannot be completely wrong. But Cecilia Chillenti, a physicist at the University of Maryland in Parker who was not involved in the study, said the new study "more clearly confirms" the laws of the region. So far, general relativity has described black holes well. But scientists do not fully understand what happens when general relativity (usually applied to large objects such as black holes) encounters quantum mechanics (which describes small objects such as atoms and subatomic particles).

In that quantum realm, strange things can happen. For example, a black hole can release a mist of particles called Hawking radiation. This is another idea that Hawking put forward in the 1970s. This effect can make the black hole shrink, violating the law of area, but only for an extremely long time, so it will not affect the relatively fast black hole merger that LIGO sees. Physicists are looking for an improved theory to combine these two disciplines into a new and improved theory of quantum gravity. Any failure of black holes to fail to comply with general relativity can point physicists in the right direction to find new theories. Therefore, physicists are often dissatisfied with the lasting success of general relativity, Farr said. "We thought, 'oh, it's okay again.”

The News Talkie Bureau

Source:

**Sciencenews.org**