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How could a graviton mediate gravity at places such as a black hole?

  1. Mar 12, 2012 #1
    Is there some type of exception to the singularity for gravitons? And if not gravitons then what? I understand the spacetime curvature except why does a sun not collapse in on itself right now when it does after fusion has stopped? I'm told it's from energy creating pressure outwards counteracting the inward pull of gravity but that would suggest that an interaction between particles is taking place, no? And if the pressure created by fusion pushes more against gravity than the normal matter does after fusion has stopped, should the sun not be expanding?
  2. jcsd
  3. Mar 12, 2012 #2
    In some string theories, it is my understanding that gravitons are emitted from the surface (event horizon) of the black hole.
  4. Mar 13, 2012 #3
    So there is a special exclusion..?
  5. Mar 13, 2012 #4
    Not really, it's just that instead of a singularity, it is a 'fuzzball' that is spread out more or less uniformly with the event horizon at its surface.

    Again, I have to stress that this is my understanding only, it could be highly flawed.
  6. Mar 13, 2012 #5
    If the pressure from fusion plus the pressure from the internal structure of the matter is equal to the pull from gravity, it will not collapse or expand. If the opposing forces are not equal, it will either expand or contract. Both of these things happen to a star during its normal lifespan. The contraction only turns into a complete collapse if it is a massive enough star (there may be ways for a smaller star to turn into a black hole too, but I think that is less common).

    If the star expands a bit, the pressure decreases a bit. That decrease may be enough to make the pressure be less than the gravitational pull... so a cycle begins.
  7. Mar 13, 2012 #6
    If the entire black hole is everything inside or is a sort of "solid block" from which gravitons are emitted at it's surface, the event horizon, why is it predicted you could travel down one with normal relativistic effects? It should just be the same facric ofspace crossing the border of the event horizon, and matter should follow that path, and based on our understanding matter isn't destroyed when it passes the horizon, but when it reaches the singularity.
  8. Mar 18, 2012 #7
    But what I was wondering is why it would collapse into a black hole, because even if it were massive enough, it shouldn't collapse into a black hole unless gravity was proportional to volume or pressure right? Since it's only caused by mass then once the internal pressure goes away all that's left is the mass of whatever didn't burn away and the gravity of that isn't enough to form a black hole right? Like I get that there's no internal pressure to counteract gravity but since the gravity is only based on mass, is it that the star would be a black hole if it weren't fusing things together?
    Last edited: Mar 18, 2012
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