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Black Hole and the event horizon

  1. Feb 18, 2009 #1
    This question may have been asked before becuase it seems like one of the first questions that would be asked after learning of black holes. My question is, how do gravitons escape the event horizon? They must somehow escape, otherwise the black hole could not influence anything with its gravitational pull.

    I have a few more questions on black holes.

    I have read that black holes have an infinite density, but I have also read that one of the properties of the black hole is its size. By size do they mean the size of the event horizon? Because something with infintie density becomes a point, right? If the density and curvature of spacetime is infinite, then does time stop, like it would if someone were to move at light speed, according to someone outside the event horizon?

    And finally, for black holes evaporating, does the quantum process have to happen outside the event horizon? It seems like it has to. The book I'm reading is Stephen Hawkings A Brief History of Time, which may be too brief, kinda went to fast over the black holes evaporating. So when the pair of virtual particles is produced, does the process need to happen really close to the black holes event horizon, so that one of the particles will fall into the event horizon?

    The last question I'm not really sure of, I have a feeling that I am way off.

    Thanks
     
  2. jcsd
  3. Feb 18, 2009 #2
    This link does a better job of explaining gravitons than I could.
    http://curious.astro.cornell.edu/question.php?number=264 [Broken]

    However, I think I can answer the others. When the size of a black hole is discussed it is generally talking about the event horizon. Inside the event horizon since nothing can escape it doesn't make sense to talk about what's inside. I believe that time does stop at the event horizon.

    You seem to have the right idea about Hawking Radiation. Two particles appear, and normally destroy each other and no net gain or loss of energy occurs. When this happens close to a black hole one is pulled into it, and the other escapes, since there is a net gain from this it must come from somewhere, and the black hole loses mass equal to the particle that got away.
     
    Last edited by a moderator: May 4, 2017
  4. Feb 19, 2009 #3
    Thanks for the reply Dale, the link was very helpful:smile:
     
  5. Feb 19, 2009 #4
    Not true.
    You can jump into the black hole, and time will not stop for you
    In fact, you can cross a horizon of a super-massive BH without even noticing it.
     
  6. Feb 19, 2009 #5
    Actually DaleSwanson and Dmitry67 are both right. It depends on one's perspective. To a distant observer, time does stop at the horizon. To the falling object, time seems normal.
     
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