The physics of black holes is still surrounded by many unsolved questions. For example, we know that two black holes can merge to form a larger one, but can a larger black hole split into two smaller ones? Traditionally this is not thought of, because it would go against the laws of physics. However, a team of scientists from the Federico II University of Naples, the Sorbonne in Paris and the University of Southern Denmark have just found a theoretical shortcut that would make this possible.
A matter of order. According to the second law of thermodynamics, the entropy of an isolated system always increases. Broadly speaking, entropy refers to the number of disorder or different microscopic conformations that a system can attain. Therefore, it is always said that the universe tends towards disorder.
Generally, in most objects, entropy is proportional to the amount of matter, so if a piece of paper is torn in two, its entropy will not decrease, since the sum of the two pieces remains the same. With black holes, things change, since the entropy between them is proportional to the area of the event horizon, which increases with the square of the black hole’s invariant mass. If a black hole splits into two, the area of its event horizon will be smaller, so the entropy will decrease. It would go against the laws of physics.
turn the key. According to the authors of this recent study, there may be a way for a black hole to split in two without reducing its entropy. This can happen if it spins very fast, practically at the limit of what physics allows. This is because energy is related to mass. We all know the famous formula E=mc^2. If an object spins very fast, a fraction of its mass is invested in the energy needed to drive the spin. Therefore, since we have seen that entropy is proportional to the square of mass, for a given mass, the faster a black hole rotates, the lower its entropy.
Divided into two parts, the amount of spin known as angular momentum can vary from rotation (of a black hole on itself) to orbital angular momentum (of one object around another). As a result black holes will spin around each other, but not on themselves, so some of the mass invested in the spin will be recovered and entropy may not decrease.
They can be combined. Once a black hole splits, it can happen that the two fragments will attract each other, fall on top of each other and come back together. Therefore, the energy should be sufficient to escape from that attraction. Something similar to what happens with the escape velocity of a rocket. This makes the separation even more exceptional; But, according to these scientists, it is not impossible.
other parameters. Beyond spin speed, the study includes other parameters that would favor the theoretical separation of black holes, such as the existence of more dimensions or altered gravity.
A primordial black hole is more likely. These scientists believe that primordial black holes would have better properties for this separation to occur.
These are just calculations. It should be noted that this is all theoretical physics. It was found that, under certain conditions, calculations do not prohibit a black hole from splitting into two. However, this has not been demonstrated or observed in practice. All you have to do is say that it probably occurs in primordial black holes, and these are theoretical objects too. Still, it’s interesting to understand that physics allows this to happen. And if that really happens, we’ll see that Einstein’s laws apply very well to what we’ve observed so far, but they’ll have some gaps to polish.
Picture | P.Marenfeld and NOAO/AURA/NSF
In Xataka | Black holes are exciting. and those formed from the collision of two of them are even more so.
