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Black holes are supposed to suck everything

  1. Sep 21, 2009 #1
    if black holes are supposed to suck everything how come gravitons are emitted.
    cause to attract something gravitons should come in contact with it.
     
  2. jcsd
  3. Sep 21, 2009 #2

    mathman

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    Re: gravitons

    In the frame of outside observers the black hole never quite forms, so the gravitons are from the object before it becomes a black hole.
     
  4. Sep 21, 2009 #3

    Entropee

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    Re: gravitons

    Gamma rays are also emitted, thats how we can tell where black holes are.
     
  5. Sep 22, 2009 #4

    Hepth

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    Re: gravitons

    I think hes asking more:

    If gravitons gravitate, then how do gravitons from the center of the black hole couple to anything outside the event horizon.

    Would it make sense to be viewed as, to outside observers, all information resides on the visible surface, and by visible, I also mean gravitationally interacting.
     
  6. Sep 22, 2009 #5

    Haelfix

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    Re: gravitons

    Theres a similarity to asking how can an electron, inside a box or even a cavity, contribute anything to the exterior? Well, the answer is several ways. In the case of a neutral box it would get a charge and contribute electromagnetically, and even if it was a say a solenoid you still have 'quantum' effects such as nontrivial field configurations like the Aharanov-Bohm effect or tunneling processes.

    Similarly, gravitons have some energy and are part of the gravitational field which indeed contributes to the exterior in the usual way (blackholes still gravitate). Second, there are tunneling processes that are speculated to occur. Third, there are indeed sublte questions of exactly what you mean by a 'graviton' inside a 'black hole' in the first place.

    The exact details are of course hard to quantify, absent a general theory of quantum gravity
     
  7. Sep 22, 2009 #6

    Vanadium 50

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    Re: gravitons

    I'm sorry, but this thread is a mess. There are misconceptions on top of misconceptions here.

    The first misconception is that gravitating objects emit streams of gravitons, and these streams are responsible for gravitation. This is not true. Massive objects don't emit gravitons just like electrically charged objects don't emit photons: charged objects don't glow just because they are charged.

    The second misconception is that the fact that somehow the horizon doesn't form from the perspective of an outside observer somehow lets gravity "escape". First, even if gravity were "streaming out", the extreme time dilation would slow the streaming to zero. So this doesn't explain anything. More importantly, the gravitational field far away is the same whether a horizon forms or not, so this cannot possibly make a difference.

    The third misconception is that black holes emit gamma rays (or, more commonly, x-rays). They don't. The gas around them heats up as it falls in, and this hot gas is doing the emission.
     
  8. Sep 22, 2009 #7

    Haelfix

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    Re: gravitons

    Thats certainly true Vanadium, I apologize for responding to my own inner questions and not the OPs (who I thought was asking something else). Its worth keeping in mind that gravitons we are talking about here are necessarily virtual and not something that is emitted. So the physically interesting question is the following:

    Take two particles that might be close somehow just outside a bh. Then move one of the particles into the blackhole past the horizon, and let the other escape off. What can we say about the gravitational interaction between them?

    Typically, in flat space we'd want to draw a Feynman diagram with a graviton exchange to represent the interaction of gravity. That is no longer easy to do here or rather its subtle. What we can say, is that classically at least, the particle outside the blackhole still in a sense feels the other one (even if its now entangled with all the degrees of freedom inside the bh) simply b/c the particle inside contributes to the gravitational stress energy tensor in the usual way. Beyond that (and to justify using the graviton language in the first place) is quantum mechanics.
     
    Last edited: Sep 22, 2009
  9. Sep 22, 2009 #8

    Entropee

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    Re: gravitons

    Thanks for the correction Vandium
     
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