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Another black hole thread.

  1. May 13, 2009 #1
    Another black hole thread........

    So what exactly is the difference between a rotating black hole and an non rotating BH? Im not exactly sure what the difference is so i decided to ask the enlightened ones.

    Thanks all!
     
  2. jcsd
  3. May 13, 2009 #2
    Re: Another black hole thread........

    If you go near to a rotating black hole, you will be twisted around too.
     
  4. May 13, 2009 #3
    Re: Another black hole thread........

    The majority of black holes are rotating. This is because black holes generally form from collapsed stars (post CNO cycle and entering the point where it begins to attempt to fuse iron). Since the star has been rotating all this while, due to conservation of angular momentum, the subsequent black hole that is created must also retain that original angular momentum or in other words be rotating at the same rate.

    If I recall correctly, non-rotating BH's are merely theoretical BHs that are formed from non-rotating degenerate material. I'm not quite sure if the majority of pre-BH candidates are non-rotating but nevertheless, something that doesn't rotate before its black hole conversion will not rotate after.

    I hope that sort of helps.
     
  5. May 14, 2009 #4

    George Jones

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    Re: Another black hole thread........

    There are substantial differences between rotating and non-rotating black holes, including the following.

    1) Outside the event horizon of a rotating black hole, there is a region called the ergosphere from which is possible to extract energy from the black hole. Consider a composite particle that consists parts A and B held together by string and that has a timer and some explosives. The particle is launched with energy E_1 far from the black hole. The the timer and explosives are arranged such that after the particle enters the ergosphere (but is still above the event horizon), particles A and B separate, and A escapes to a place far the black hole while B falls into the black hole. It is possible that far from the black hole particle A can have an energy E_2 > E_1, with the extra energy extract from the rotation of the black hole. This called the Penrose process.

    2) Inside the black there there is another horizon that is a Cauchy horizon. Through any event inside the Cauchy Horizon, there exist closed timelike curves. Time travel is theoretically possible in this region! Also, there seems to be a non-crushing physical singularity at the Cauchy horizon. Non-crushing means that tidal forces won't necessarily destroy a person who falls through the Cauchy horizon.

    3) Once inside a spherical, non-rotating black hole, a person must "hit" the singularity inside. The singularity of a classical, eternal black hole is through which it is possible theoretically to fall without hitting the ring.

    It seems that classical general relativity breaks down at a rotating black hole's Cauchy horizon. This has been suspected/known for almost 40 years. It also seems that semi-classical relativity breaks down at the Cauchy horizon. It looks like this means that a fully quantum mechanical theory of gravity is necessary to predict what happens at and inside a rotating black hole's Cauchy horizon.
     
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