A merger of two black holes generating ripples in space-time called gravitational waves
Image by - New Atlas

Black holes are one of the most curiously known astronomical objects in the universe. The speciality of this object is that it doesn't let light escape from it which astronomers find difficult to locate. But they can detect the activities that happen around it which provide a lot of information about them.


Recently by studying the gravitational waves generated by the scientists were able to prove one of the famous black hole laws of Stephen Hawking.


Stephen Hawking developed the theorem in 1971 and it states that the surface area of the event horizon of a black hole cannot decrease with time. It is derived from Einstein's General Theory of Relativity.


It has fascinated physicists from around the world because this theorem is similar to the second law of Thermodynamics which states that the disorder or the entropy of a system cannot decrease with time instead, it always increases consistently. It also obeys the law of conservation of mass which follows the law of conservation of energy. 


Astrophysicist Will Farr of Stony Brook University in New York & the Flatiron Institute in New York City says that "it's an exciting hint that black hole areas are something fundamental & important."


Nothing can escape from within a black hole therefore the surface area of its event horizon cannot change. However, if it engulfs some matter or energy due to its strong gravitational pull then it gains more mass which increases its surface area and also it's spin which in turn decreases the surface area.


The area theorem states that the increase in surface area due to the added mass will always be greater than the decrease in surface area due to the additional spin. 


To prove this theorem, MIT astrophysicist Maximiliano Isi, Will Farr & other scientists observed the ripples in space-time generated by two inwardly spiralling black holes that merged to form a bigger black hole. 


According to the area theorem, the surface area of the event horizon of the new black hole should be equal to the combined surface area of the event horizon of the two original black holes. 


The researchers also analyzed the data from the first gravitational waves that were detected by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, in 2015.


They split the gravitational waves data into two-time segments, before & after the merger & calculated the surface area of the event horizons in each segment. The surface area of the new black hole came out to be greater than the combined surface area of the two initial black holes thus proving the area theorem right. 


The team reports in a paper that will appear in Physical Review Letters. "It's the first time that we can put a number on this", Maximiliano Isi said. 


Conclusion 


Stephen Hawking's area theorem is the result of Albert Einstein's General Theory of Relativity. Previous analyses of the gravitational waves agree with the predictions of general relativity but the scientists don't fully understand what will happen if this is applied to quantum mechanics where strange things happen.

 

Therefore, they are finding an improved theory that will combine the two realms into one new complete theory of quantum gravity. If the black holes fail to abide by the rules of general relativity then this could push the physicists to find that theory. That's why they tend to be grumpy about the continuous success of Einstein's Relativity. Will Farr says, "We were like awe, it was right again".