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Black hole existence

  1. Feb 26, 2008 #1
    Hello! Can anyone help me with the following question about black holes?

    Let us consider a massive star which at the end of its evolution collapses into a black hole (say a Schwarzschild black hole, for the sake of simplicity). An observer far away, in its coordinate time, will never see the collapse because it would take an infinite amount of time for the star to reach its event horizon.
    On the other hand, the black hole forms because the amount of proper time would instead be finite.
    Since we are able to detect black holes (from indirect observations), should we infer that they are eternal? And if they are eternal, how does this possibly match with Hawking radiation (their mass should be infinite and they cannot evaporate)? Is it possible that what we see are still forming black holes?

    Thank you very much!
  2. jcsd
  3. Feb 26, 2008 #2
    I am not an expert in this, but I think it is the other way around. If you happened to be within the black hole's event horizon, you would never see it happen (because time would dilate so extremely that the collapse just never quite eventuates).

    If you were outside the black hole's event horizon you couldn't share the same frame as someone inside it. The formation of the black hole would continue at its "normal" pace from a sufficiently distant outside observer's point of view.

    (I don't think that boundary events are really of much significance, if you want to bring up two observers with neglible separation, one inside the event horizon and one outside the event horizon. That is, I don't think there would be a noticeable transition between outside and inside. I may be wrong, not having first hand experience.)


  4. Feb 26, 2008 #3

    George Jones

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    We detect signals from phenomena that occur near objects that are in the very, very late stages of their collapse to black holes.
  5. Feb 26, 2008 #4
    No, there is no transition. The event horizon is not a real singularity, in fact it does not exist in Kruskal coordinates (I think). But a far-away observer sees the event horizon actually as a barrier (this is due to his reference frame).

    So we actually see still forming black holes!

    Thank you very much!
  6. Mar 2, 2008 #5
    I am indeed a amateur when it comes to Quantum Physics, However I would say the the event horizon and the black hole itself is formed almost instantly and this is not something that we observe forming over a great period of time. As observers we see the beginning of activity, meaning that the black hole is at its absolute maturity almost indefinitely. I must also explain that the undefined Cosmic jets are indeed the "other side" of what we have seen. Therefore no matter has disappeared and the universe itself has remained equal. As I have said I am an amateur but very curious what others have to say of my view. I understand that science is not always logical but, this seems to make sense to me.
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