3
$\begingroup$

I am not an expert, I was just thinking about this scenario:

A black hole that, for some reason, will start spinning faster and faster. Is it theoretically possible that the rotation becomes so fast that the centrifugal force overcomes the gravitational attraction, causing the black hole to explode?

Gravitation is a weak force, while centrifugal force is much stronger...

$\endgroup$
1
  • 1
    $\begingroup$ Centrifugal force depends on the radius, and a black hole doesn't have a known radius. Matter inside a black hole may not be in in a state that has a size in any way that is comprehensible to newtonian physics. The very concept of rotation has similar issues. (If it has zero radius, how would you even define 'rotate'?) A black hole must have rotational momentum but how that's expressed on the material inside the event horizon is pretty much undefined. $\endgroup$ Feb 14 at 18:49

2 Answers 2

4
$\begingroup$

There is in fact an upper-limit to the angular momentum of the black hole that is described by the Kerr solution. If a black hole existed with a higher angular momentum, you'd have a singularity outside of the event horizon, which is usually considered something that can't happen in reality. The way it works intuitively is that a rotating black hole causes "frame dragging" in the space around it such that when the black hole is at the limit of angular momentum, any in-falling object that you might suppose would add angular momentum, because of the frame dragging, couldn't be in a trajectory where it would cross the event horizon.

This paper provides a "simplified" description: https://www.eftaylor.com/pub/SpinNEW.pdf

$\endgroup$
1
  • 1
    $\begingroup$ Added this before I saw the duplicate for this question, which explains it much more thoroughly and precisely. $\endgroup$
    – antlersoft
    Feb 15 at 14:11
2
$\begingroup$

No.

Consider what "explode" would mean in this context: It means each piece of material tears away and exits the black hole. By definition, that simply can't happen. The material would need to be moving faster than the speed of light in order to cross the event horizon, and we know that's impossible.

$\endgroup$
3
  • 2
    $\begingroup$ You say this as if its trivial. In reality it was quite a "tour de force" to prove black holes cannot be "overspun". $\endgroup$
    – TimRias
    Feb 14 at 19:12
  • $\begingroup$ I'd be happy to see it if you can provide an answer with more basis in the physics of it -- the mathematics of black holes is a bit beyond me, personally. I assume as the rotational energy increases, eventually the black hole would start acting like it was gaining mass, making it harder and harder to accelerate, the same way particles act if you try to accelerate them close to c, but that's just me thinkin'. $\endgroup$ Feb 14 at 19:38
  • 1
    $\begingroup$ The EH (event horizon) is often described as a speed barrier, but that just shifts the question from "why can't you escape the EH?" to "why can't you go faster than light?". Due to spacetime curvature, any light or matter inside the EH must move towards the centre. The only paths crossing the EH go from outside to inside. So now the question becomes "why can't you go backwards in time?". ;) I have some more on this topic here: physics.stackexchange.com/a/696441/123208 $\endgroup$
    – PM 2Ring
    Feb 16 at 2:37

Not the answer you're looking for? Browse other questions tagged .