4

If the star's mass supposedly collapses into a single point, and it ends up having "said" zero volume, then how can people say that the hole has a specific spin or that it can have an angular momentum?

Does it mean that the singularity is somehow still spinning, or maybe the spacetime around it is just being dragged for some reason?

Qmechanic
  • 201,751
Murtuza Vadharia
  • 1,807
  • 3
    Murtuza, I've linked a question that addresses your point. The tl;dr answer is that in a rotating black hole the singularity is a ring not a point. – John Rennie Dec 04 '14 at 18:02
  • @JohnRennie isn't the classical understanding that it is an extremely thin disk? I know things are actually more complex than that, but I don't think I've heard "ring" used to describe them before. – zachaysan Dec 04 '14 at 22:06
  • @zachaysan: no, it's a ring – John Rennie Dec 05 '14 at 06:31
  • @John Rennie are there any pictures explaining ring singularity which you can post as answer for better understanding.... – Murtuza Vadharia Dec 08 '14 at 15:59
  • @MurtuzaVadharia: understanding the Kerr metric is one of the more challenging tasks for aspiring general relativists. You aren't going to really understand its structure without a lot of hard work. I'm afraid there is no quick and easy route. – John Rennie Dec 08 '14 at 16:55

1 Answers1

3

In short: the laws of conservation (angular momentum, charge, mass-energy, etc.) still work during the process of creation of a black hole. So if a star had some angular momentum/charge before it collapsed, the resulting black hole will also have some (assuming the angular momentum/charge was not radiated away during the collapse).

Also, the claim that black holes have "zero" volume is simply incorrect.

yohBS
  • 1,755