What will the merger of black holes lead to? The increased mass will make the result of the merger dense and compact or the new black hole will become larger? British cosmologist and astrophysicist Stephen Hawking answered this question half a century ago, long before the discovery of gravitational waves.
It is generally believed that the behavior of black holes obeys simple laws, and modern science is gradually confirming this. Scientists, in particular, managed to confirm the black hole law, which was predicted by Stephen Hawking in his time. The latter back in the seventies of the last century proposed a theorem about the area of a black hole, according to which the area of such an object cannot decrease over time. Hawking’s theorem reflects a long-known rule – entropy of a closed system cannot decrease.
The area of a black hole does not change unless new matter enters it. But what if black holes merge? There was an assumption that the resulting object would become denser and more compact, but this contradicts Hawking’s theorem, which gravitational waves have shown to be true.
Scientists from the Massachusetts Institute of Technology (USA) studied gravitational waves recorded by the Advanced Laser Interferometer observatory in 2015 and divided them into ripples in space-time before and after the merger of black holes. Determining the areas of the black hole surfaces showed that the object that formed as a result of the merger acquired a larger area than the areas of the original objects.