HAWKING’S THEORY ABOUT BLACK HOLE AREA CONFIRMED

One of Stephen Hawking's most famous theorems has been proven right, using ripples in space-time caused by the merging of two distant black holes, Ben Turner reported for Live Science.

The black hole area theorem, which Hawking derived in 1971 from Einstein's theory of general relativity, states that it is impossible for the surface area of a black hole to decrease over time.

This rule interests physicists because it is closely related to another rule that appears to set time to run in a particular direction: the second law of thermodynamics, which states that the entropy, or disorder, of a closed system must always increase. Because a black hole's entropy is proportional to its surface area, both must always increase.

According to the new study, the researchers' confirmation of the area law seems to imply that the properties of black holes are significant clues to the hidden laws that govern the universe.

Oddly, the area law seems to contradict another of the famous physicist's proven theorems: that black holes should evaporate over extremely long time scale, so figuring out the source of the contradiction between the two theories could reveal new physics.

"A black hole's surface area can't be decreased, which is like the second law of thermodynamics. It also has a conservation of mass, as you can't reduce its mass, so that's analogous to the conservation of energy," lead author Maximiliano Isi, an astrophysicist at the Massachusetts Institute of Technology (MIT), told Live Science.

"Initially people were like 'Wow, that's a cool parallel,' but we soon realized that this was fundamental. Black holes have an entropy, and it's proportional to their area. It's not just a funny coincidence, it's a deep fact about the world that they reveal."

A black hole's surface area is set out by a spherical boundary known as the event horizon — beyond this point nothing, not even light, can escape its powerful gravitational pull.

According to Hawking's interpretation of general relativity, as a black hole's surface area increases with its mass, and because no object thrown inside can exit, its surface area cannot decrease. But a black hole's surface area also shrinks the more it spins, so researchers wondered whether it would be possible to throw an object inside hard enough to make the black hole spin enough to decrease its area.

"You will make it spin more, but not enough to counterbalance the mass you've just added," Isi said. "Whatever you do, the mass and the spin will make it so that you end up with a bigger area."

To test out this theory, the researchers analyzed gravitational waves, or ripples in the fabric of space-time, created 1.3 billion years ago by two behemoth black holes as they spiraled toward each other at high speed.

These were the first waves ever detected in 2015 by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), a 1,864-mile-long (3,000 kilometers) laser beam capable of detecting the slightest distortions in space-time by how they alter its path length.

By splitting the signal into two halves — before and after the black holes merged — the researchers calculated mass and the spin of both the two original black holes and the new combined one. These numbers, in turn, allowed them to calculate the surface area of each black hole before and after the collision. The researchers published their findings May 26 in the journal Physical Review Letters.

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