## What happens when two black holes collide?

For the first time, we have observed a 50-year-old Stephen Hawking theorem in the natural world. Scientists from the Massachusetts Institute of Technology (MIT), the California Institute of Technology, Cornell University, and Stony Brook University analyzed gravitational wave data from two inspiring black holes. What they found in the collision proved Hawking’s area theorem: the area of ​​the event horizon of a black hole cannot be reduced.

When a binary black hole system is inspired, the orbits of the two black holes shrink and the system begins to emit gravitational waves. The emission rate increases as the orbits shrink further and gain speed, and when fusion finally occurs, the emission of waves peaks. The two black holes become a single new black hole, and according to Hawking’s theorem, that new black hole should have a surface area equal to that of the original two black holes. That’s exactly what the researchers found based on the observed inspiration system wave data.

The confirmation brings us closer to understanding the ins and outs of black hole functions, says Dr. Riccardo Penco, associate professor of High Energy Physics Theory at Carnegie Mellon University. “Detecting gravitational waves allows us to test black holes directly (rather than just inferring their existence indirectly by studying the motion of other objects around them). For a long time, we have studied black holes as mathematical objects endowed with a remarkable set of properties (Hawking’s area law is one of them). We are now in a position to test these properties experimentally. “

According to Hawking’s calculations, if a black hole changes area, its event horizon would stretch or narrow in correspondence with its new size. The event horizon, the area of ​​effect of a black hole’s gravitational field, is the point of no return for anything – including light – orbiting the black hole. An object would have to travel faster than the speed of light in order to escape.

Penco claims that Hawking’s Theorem is valid for black holes observed by the Laser Interferometer Gravitational Wave Observatory (LIGO) – a pair of US facilities built to study gravitational waves – whose work these researchers used for their findings. But Hawking’s Theorem could also be applied to other black holes, those that at first seem to defy the Theorem until they prove applicable to another concept hypothesized by the physicist.