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From my (somewhat limited) understanding of GR I know that there are two different kinds of solutions that produce a black hole, some that rotate and some that do not. What I can't figure out from my reading so far is which of the two is considered "typical" (if either). That is, when we think we have detected a black hole in space, do we initially suspect that it's rotating or static?

My naive assumption would be, since they form from collapsing rotating stars, that most black holes would continue rotating after formation, increasing in speed as they decreased in volume. However, I see a lot of discussion about black holes that use Schwarzschild's equations, which describes a non-rotating object. Is this merely because those are easier to deal with and "close enough", or is it really believed that many black holes are non-rotating?

Qmechanic
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KutuluMike
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1 Answers1

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Well, I have been working on Black Holes for nearly 3 years now. And you are partially right in assuming that rotating stars lead to rotating black holes. The actual dynamics is much more complex, as it is the core of the star which needs to have angular momentum after going hypernova.

Rotating black holes have a region around them, called the 'ergosphere'. In principle, we can extract energy from the ergosphere via a process called 'Penrose process'. And when we have extracted a maximum amount of energy, the black hole starts to lose its angular momentum, like a top, and soon comes to be non rotating.

Also, there are 4 solutions to the types of black holes. Not 2.

Abhiram
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