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I What problems would 'black holes' not being formed solve?

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  1. Jul 21, 2018 #1
    So when a star collapses, if the event horizon doesn't form, but the object remains in ordinary space, in increasing gravitational time-dilated collapse, what problems with these objects would be solved or more easily addressed?
    I would think at least the information loss problem, and then there is the conservation of rotational momentum, and then there is the production of the magnetic field.
     
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  3. Jul 21, 2018 #2

    mathman

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    Your question is about a physically impossible situation. It seems very hard to answer.
     
  4. Jul 21, 2018 #3
    As mathman already mentioned, the event horizon will always form in such a collaps. But I wonder if the singularity could be avoided. Is it possible that the black hole evaporates before the singularity forms?
     
  5. Jul 21, 2018 #4

    Chronos

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    In a classical sense a singularity is the inevitable result of gravitational collapsei of any sufficiently massive body. Ir is not entirely clear if a gravitational singulariy is the truly the physical consequence of such an event. There is no real disseny over the formation of an event horizon. There is good reason to doubt this happens even if quantum corrections conspire to preclude the formation of a singularity. Whether or not an event horizon is accompanied by a singularity does not appear to be relevant to event horizon properties given there is little to suggest a singularity is even necessary
     
  6. Jul 21, 2018 #5

    stefan r

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    My impression was time dilates to infinity as you approach an event horizon. Assuming I understood that correctly then a falling particle would not make progress until the black hole evaporates enough to allow progress.

    The singularity is there anyway. I thought this was the reason for the no hair theorem.
     
  7. Jul 21, 2018 #6

    phinds

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    Your impression is wrong. Objects fall through the event horizon as thought nothing is there because in physical terms, that is exactly correct. Nothing is there. You can't get back out again after you cross it, but other than that it really doesn't exist.
     
  8. Jul 21, 2018 #7

    phinds

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    The time dilation of which you speak is an observational phenomenon of an observer far removed from the BH, not something that happens to the infalling object.
     
  9. Jul 22, 2018 #8
    but say that 'something' does prevent the event horizon forming, what problems with these objects would be addressed in part, or in full?
     
  10. Jul 22, 2018 #9

    phinds

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    This question amounts to "if the laws of physics did not apply, what would the laws of physics say about <insert nonsense of your choice>?"
     
  11. Jul 22, 2018 #10

    Chronos

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    They could comprise part of the macho population contributing to the DM budget without violating gamma ray background constraints imposed by observational astronomy. They could also cause gravitational lensing and possibly waves without triggering EM emissions, or basically a variety of phenomena.that are not necessarily accompanied by significant EM events. Keep in mind, however, that gravitational collapses are not entirely free from collateral consequences
     
    Last edited: Jul 22, 2018
  12. Jul 23, 2018 #11

    stefan r

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    We have found objects that collapsed and did not form an event horizon.
     
  13. Jul 23, 2018 #12
    Yes I have heard of neutron stars. I was rather meaning objects in a continual state of collapse, that would usually be considered to form event horizons.

    Or alternatively, if you like, you could considered an unknown force/process, which prevents the object from collapsing enough to form an event horizon.

    I find it more intuitive to imagine an object conserving its angular momentum if it remains an actual object. Plus, as I mentioned, the generation of the magnetic field.
     
  14. Jul 23, 2018 #13
    The problem is not with event horizons. Any body with an escape velocity of at least c will necessarily form an event horizon, there is no doubt about this, as it's inevitable. The question is whether there is an actual physical singularity "behind" the horizon or not.
     
  15. Jul 23, 2018 #14

    Nugatory

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    Yes, but these do not collapse past their Schwarzschild radius, so General Relativity predicts that an event horizon will not form. It's only if the collapse reduces the size of the object to less than that radius that we expect the horizon to form.
     
  16. Jul 23, 2018 #15
    https://en.wikipedia.org/wiki/Magnetospheric_eternally_collapsing_object

    "...He argued that all proposed black holes are instead quasi-black holes rather than exact black holes and that during the gravitational collapse to a black hole, the entire mass energy and angular momentum of the collapsing objects is radiated away before formation of exact mathematical black holes ... Mitra argues that he has proven that the world-line of an in-falling test particle would tend to be lightlike at the event horizon, independent of the definition of "velocity"."
     
  17. Jul 23, 2018 #16

    mathman

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    There is plenty of evidence for the existence of black holes, very large ones at the centers of galaxies and companions in some binaries. Speculations involving physics which contradict observations are pointless.
     
  18. Jul 23, 2018 #17
    But how would the observations differ between an event-horizon black hole and the above given magnetosphere eternally collapsing object?
     
  19. Jul 23, 2018 #18

    mathman

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    I'm missing something. What is "magnetosphere eternally collapsing object"?
     
  20. Jul 23, 2018 #19
    the one in post #15.
     
  21. Jul 23, 2018 #20

    Chronos

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    Without venturing too deeply into the swamp, it is safe to say Einstein was opposed to the notion that an event horizon could be physically realized without a singularity forming. And the fact most physicists are opposed to the notion that a singularity can be physically realized leaves very much a conundrum. Suffice it to say the easiest trap to fall into [aside from a black hole] is an unfortunate choice of reference frame and inconsistent usage throughout a solution that results in realization of an event horizon. I am not aware of any widely accepted solution for this problem, but, am resist the notion that such a solution is not possible. We know that a neutron star can get close to forming an event horizon [depending, of course, on how strictly you elect to define 'close'] so I am willing to concede it should be possible to span the remaining gap without defying the currently known laws of physics.
     
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