# Increase in spin rate as object collases to black hole

1. Nov 30, 2009

### hexexpert

It has been said that physics still occur inside a black hole, excluding the singularity. It's just that we can't observe the physics. The spin of black hole is measurable. What I want to know is; does the INCREASE in spin as the object gets ever smaller stop increasing at the moment in becomes a black hole? Certainly the spin doesn't increase to infinity. If the observed spin did continue to increase for a bit before coming to a stop would this would imply a hard radius below the event horizon? Has this been specifically excluded? If anyone has a link to the subject of spin as an object transitions to becoming a black hole I'd appreciated it.

2. Nov 30, 2009

### Jonathan Scott

You can't observe the frequency of the spin. You can observe the angular momentum (by its frame-dragging effect), but that is constant in the absence of external interactions.

3. Nov 30, 2009

### Staff: Mentor

Also, the singularity in a
Kerr black hole is not the same as the singularity in a Schwarzschild black hole. It is called a ring singularity because it does not collapse down to zero radius.

4. Dec 4, 2009

### stevebd1

You might find this link of interest-

http://people.sissa.it/~rezzolla/Whisky/WhiskyI/ [Broken]

Last edited by a moderator: May 4, 2017
5. Dec 4, 2009

### xantox

If the body undergoing collapse is rotating too fast in the first place (eg above the Kerr limit), then it will not collapse into a black hole. If it collapses, the only externally observable property describing its rotation is the angular momentum, which is a conserved quantity (it can increase or decrease if the black hole is not isolated).

Interiors of realistic spinning black holes remain a hard and vastly unexplored topic. A seminal paper by Poisson and Israel [1] presented the theory of mass inflation: the unstable inward and outward pressure and energy flows near the inner lightlike horizon should enter a runaway amplification due to their own gravitational effect – this could be indeed a form of "hard radius" where most infalling matter could smash into before a further collapse.

[1] E. Poisson, W. Israel, "Internal structure of black holes", Phys. Rev. D 41, 1796–809 (1990).

Last edited: Dec 5, 2009