Spin of Black Holes: How Does it Affect Collapse?

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    Black hole Hole Spin
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Discussion Overview

The discussion revolves around the effects of spin on black holes, particularly focusing on the nature of singularities in rotating black holes (Kerr black holes) and the implications of angular momentum during collapse. Participants explore theoretical concepts, hypotheses, and the relationship between spin and black hole characteristics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that if a collapsing object has initial spin, its spin should approach infinity as it collapses to a singularity, drawing an analogy to an ice skater.
  • Another participant introduces Kerr black holes, noting that they possess ring or toroidal singularities rather than point singularities, and that angular momentum is associated with their spin.
  • There is a question about the existence of wormholes associated with spinning black holes, with one participant asserting that this idea lacks scientific basis and may stem from science fiction.
  • A participant expresses curiosity about why Kerr black holes do not have point singularities and expects angular momentum to increase during collapse, seeking further elaboration.
  • One participant discusses the mathematical properties of the Kerr metric, noting that certain calculations indicate no singularity exists unless approaching along specific planes, leading to the concept of a toroidal singularity.
  • There is a discussion about the prevalence of non-spinning black holes, with one participant questioning why not all black holes are Kerr black holes, suggesting that very low spin black holes can be approximated by the simpler Schwarzschild solution.

Areas of Agreement / Disagreement

Participants express differing views on the nature of singularities in black holes, the existence of wormholes, and the implications of spin. There is no consensus on these topics, and multiple competing views remain present in the discussion.

Contextual Notes

Some mathematical steps and assumptions regarding the properties of Kerr black holes and the conditions under which singularities are defined remain unresolved. The discussion also highlights the complexity of black hole metrics and their implications for understanding spin.

tony873004
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I was just discussing a paper about the spin of a black hole and it made me wonder.

If the object that collapsed into a black hole had some spin to begin with, and a collapsing rotating object spins faster like the ice scater pulling her arms towards her body, then as the size approached 0 (singularity), shouldn't the spin approach infinity?
 
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Look up Kerr black holes. These are the ones with spin. they do not have point singularities but ring or torodal ones the angular momentum is in the spin. See also the topic "view from a ring singularity" on this topics page
 
i've heard that spining bhs have wormholes. is it right? i know that this worm hole stuff hasen't been proved. i think this is just a hypothesis. is this true?
 
i've heard that spining bhs have wormholes. is it right? i know that this worm hole stuff hasen't been proved. i think this is just a hypothesis. is this true?

No, there is no sciencific basis for that at all. In fact, I think it is straight out of some sci-fi movie from the 60's.
 
Soul Surfer said:
Look up Kerr black holes. These are the ones with spin. they do not have point singularities but ring or torodal ones the angular momentum is in the spin. See also the topic "view from a ring singularity" on this topics page

I am not very well informed on Kerr black holes. Why don't they have point singularities? And even if they don't I still expect the angular momentum to increase as they collapse. Can someone elaborate?

Thanks!
 
When you're working with the Kerr metric and you compute [tex]R^{abcd}R_{abcd}[/tex] you end up with (assuming no charge, otherwise it's horrific according to my lecturer) [tex]R^{abcd}R_{abcd} = \frac{48m^{2}}{(r^{2}+a^{2}\cos^{2}\theta)^{2}}[/tex]. This is never singular unless you approach the black hole along the equatorial plane [tex]\theta = \frac{\pi}{2}[/tex].

As such, if you fall into the black hole off this plane, then you can actually go to a region with r<0, because from your point of view no singularity exists at r=0. Hence, you end up with a toroidal singularity which exists in the equatorial plane.

If you're familiar withg Penrose diagrams, you can show that moving in such a fashion takes you into another asymptotically flat space-time, but separate from your original space time.

The toroidal singularity also have a region around it where causality is broken too.

I'm just going on my lecture notes on my desk, so not terribly familiar with it myself.
 
It's hard to imagine any objects in the universe whose spin rate is 0.00000...
So why aren't all black holes Kerrs?
 
tony873004 said:
It's hard to imagine any objects in the universe whose spin rate is 0.00000...
So why aren't all black holes Kerrs?

They probably are, technically, but if the spin is sufficiently small, the Schwarzschild solution will be a good approximation. The metric and orbits of a Schwarzschild black hole are much simpler, so that's often the only type of black hole you'll hear about from people interested in black hole phenomenology.
 

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