Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Increase in spin rate as object collases to black hole

  1. Nov 30, 2009 #1
    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. jcsd
  3. Nov 30, 2009 #2

    Jonathan Scott

    User Avatar
    Gold Member

    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.
  4. Nov 30, 2009 #3


    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.
  5. Dec 4, 2009 #4
    You might find this link of interest-

    http://people.sissa.it/~rezzolla/Whisky/WhiskyI/ [Broken]
    Last edited by a moderator: May 4, 2017
  6. Dec 4, 2009 #5


    User Avatar
    Gold Member

    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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook