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Black holes again

  1. Dec 27, 2005 #1
    This may sound silly but is it possible to see a black hole grow, how do we know that black holes consume and hold onto most of what they attract. Unseen by us could blackholes convert ordinary matter into something unknown like dark matter made from wimps for example, which are immediately re-emitted back out into space.
    Last edited: Dec 27, 2005
  2. jcsd
  3. Dec 29, 2005 #2
    Well it is all just a theory right now, we are not totally sure if black holes can do anything at all. But from the fact that there is no light in a small circlular area has to mean something. And if the black hole does take things in it has to put it some place. So what you are getting at is a really tough question that will be answered sometime.
  4. Dec 29, 2005 #3


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    Two comments:

    1) Black holes have never been directly observed in the sense that DyeeyD suggested: as a "blank spot" in a field of stars. Instead, they are detected indirectly by the emissions of matter, outside the hole, which is heated as it falls inward toward the hole. Such matter is in the so-called "accretion disc" which surrounds the black hole itself.

    2) Nothing which falls into a black hole (i.e. which crosses the event horizon) ever comes back out. Nothing, in any form, even massless photons, can escape from within a black hole's event horizon.

    Hawking radiation is a process by which a black hole can appear to lose mass, but it is a fundamentally quantum-mechanical process which actually happens immediately outside a black hole's event horizon. Once inside, nothing ever gets back out.

    - Warren
  5. Jan 4, 2006 #4
    Thankyou for the replies

    As its impossible to see anything cross through the Event horizon , how do we know that anything does, Is it just a theory,is there any proof.

    if its true that nothing can come out of a black hole as nothing can cross out wards through the EH, how does the mass inside affect the space outside, why isn't the effects of the mass at the singularity confined to the singularity side of the EH
    Last edited: Jan 4, 2006
  6. Jan 5, 2006 #5


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    1. It would be possible, in theory. We don't currently have any black holes close enough, or any telescopes large enough, to actually "observe" such an event, however.

    2. This is correct. Once inside the event horizon, all possible futures end at the singularity. To the outside world, the black hole appears gravitationally to be a mass like any other. In the same way, the Sun would influence the Earth in the same way no matter what substance it were made of. Technically speaking, in the limit of large distances, effects like tidal forces become negligible; the only important gravitational characteristic of a distant body is its mass.

    - Warren
  7. Jan 14, 2006 #6

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    Hawking radiation, if correct, is a process by which a small black hole does lose mass. Hawking radiation occurs on the very threshold of the event horizon. The concept remains controversial; it is still viewed as a conjecture by many.
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