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Some clarity on Black Hole Theory and Observations.

  1. Dec 16, 2011 #1
    Good Afternoon,

    I wonder if someone might help me understanding the current situation with regards to Black Holes.

    I understand that we have theorised about black holes, singularities in our Universe and what they do is "suck" everything within a certain range into it.

    I am not sure as to what the prevailing wisdom is for what happens to the matter that is "consumed" by the black hole.

    My understanding was that at the other side of every black hole would eventually be another universe where the consumed matter was "deposited" once a "variable status" ( variable because not all Universes need contain the same amount of matter some small and some massive) had been obtained in that singularity resulting in the destruction of that black hole in the source universe (without necessarily the destruction of the host universe) and the "creation" of the new universe "on the other side". In the newly created universe this event would be observed as something approximating the big bang i.e. something has appeared to show up from nothing and everywhere at the same time. However, I have been unable to locate any theories proposing this sort of thing to read more into it. It may be simply a figment of my imagination in which case that is fine.

    I am also not certain whether there has yet been definite observational evidence for Black Holes yet or not. I understand the inherent problems in observing them but just wanted to clarify if there has been a widely accepted observation event yet with the associated published data.

    I greatly appreciate your time and effort in replying to my question and hope that this has not already been addressed in other threads. I did perform a search of the forum and was unable to indentify an answer to my question.

    Many Thanks

  2. jcsd
  3. Dec 16, 2011 #2
    Hello Graham, welcome to the PF.

    My understanding is that black holes are simply objects where matter has become so dense that not even light can escape from them due to their gravity. I dont see any need for other universes or gateways of some kind. Also most believe that there isnt even a true singularity at their center. It is probably the boundary from which matter or energy can never return which makes them seem mysterious, however they are very much still in our universe.

    Last edited: Dec 16, 2011
  4. Dec 16, 2011 #3
    Further to Tanelorns comments:

    There are no obsered "white holes" in our Universe, so it is not a likely assumption that our black holes are the time reversals of white holes.

    Black holes are simply objects whose escape velocity exceeds the speed of light - looking at it in a purely newtonian sense.

    Black Holes have not been directly observed - as this is not possible, but what we can see are the gravitational effects which can actually be quite bright (such as stellar matter in the BH accretion disk.)

    Any discussion as to what happens to objects that pass into the BH is pure speculation, anything that passes over the EH becomes causally disconnected from our Universe. The singularity is the theorised point where density becomes infinite - most physicists nowadays believe there is no such thing as the singularity and this merely shows there is a fundamental flaw/missing link in current understanding.

    I hope this helps.
  5. Dec 21, 2011 #4
    Hi there,

    Just need to add something.......

    A black hole is nothing but a massive star having minimum 1.7 times more mass than our sun and when that star ceases of the fuel and burst with a supernova explosion its matter start condensing and thus forms a schwartschild radius and it means that when a schwartschild radius the matter got collapsed in its own gravitational pull and thus gravitational pull increases which makes it so adverse that not even light has the speed to overcome the gravitational pull of that object and hence it cannot be seen so given a name BLACK HOLE.

    Please tell me if I am wrong on this aspect.
  6. Dec 21, 2011 #5


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    Pretty close, but the Chandrasekhar limit is closer to 1.4 times the mass of the sun, and stars with mass larger than that can either form a white dwarf, neutron star or black hole. If the mass of the remnant left after the supernova is above 3-4 solar masses, then you inevitably get black holes (the Tolman–Oppenheimer–Volkoff limit).

    I would be more inclined to define black holes as a particular set of solutions to the Einstein field equations, but your definition is also good.
  7. Dec 21, 2011 #6


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    This may describe how a black hole forms, but it does not put its finger on the qualifiable difference between ordinary matter and degenerate matter that we believe exists at the singularity. There is too much matter in too small a volume to be reconciled in our equations. At some point, near the centre of a black hole, the equations simply stop working. We call this the singularity.
  8. Dec 21, 2011 #7


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    The object at the centre of our galaxy has a known minimum mass and a known maximum radius. While we can't say we've seen a black hole, we can say there's an object of the right density.
  9. Dec 21, 2011 #8
    Hi Dave,

    You are absolutely right about the centre of the black hole but the thing is when a matter cross the event horizon it become out of our physics.


    In this it states that place where singularity occurs it has infinite mass and zero volume

    But is this possible to have place with infinite density and zero volume..........I think it is not possible to create a place where this is possible even if you condense a matter to any magnitude.

    Well anyway I think it will going to be a nice conversation with you regarding the subject of black hole.


    Vinay Jain
  10. Dec 21, 2011 #9


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    Yes, but what the word "singularity" really MEANS in this context is "the place where the math starts giving us infinite answers so we don't really know WHAT is going on". So you are probably right, although we won't know until we DO know what the "singularity" really is.
  11. Dec 22, 2011 #10


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    Well, although we can't really speculate at what happens at super high densities, as matter approaches some type of singularity configuration, the nice thing about this is that in order to do black hole physics this doesn't actually matter. Since what goes on inside the event horizon can (by definition) have no causal relationship to the outside world, it is completely irrelevant. Once you've said there is a certain mass M within a volume V and we know that it's greater than the schwarzschild density, it's a black hole, case closed.
  12. Dec 22, 2011 #11

    You are absolutely right about how a black hole is identified but can u please tell me one thing

    What is the procedure to define the distance of black hole from us, is there any kind of light specturm present near black hole?
  13. Dec 22, 2011 #12
    Definition of its position can be obtained mainly using the gravitational effect on nearby masses.
  14. Dec 22, 2011 #13


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    Outside the actual event horizon, a black hole is just another massive body. We can't see inside a star but we have no trouble determining where one is.

    While it is common to say BHs can;t be seen directly, this is a bit of a overstatement. BHs tend to be surrounded by infalling dust and gas in an accretion disk, and this can be very bright indeed, especially in the X-ray band.
  15. Dec 22, 2011 #14


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    Actually, you have that exactly wrong (backwards). ALL we can do in that case is speculate. What we can't do at present is KNOW.
  16. Dec 22, 2011 #15


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    Perhaps I should have said that we shouldn't speculate :)
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