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Black hole of dark matter

  1. Jan 8, 2010 #1
    Has gravitational collapse of cold dark matter been considered? Since it can't repel (can it? thro' what interaction?) shouldn't it always go to a BH? How can it get rid of ang. momentum if it can't radiate? Maybe thro' jets... Have these things been considered?
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  3. Jan 8, 2010 #2


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    It can't get rid of its kinetic energy, too. That makes it difficult for it to form dense objects.
  4. Jan 8, 2010 #3


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    Dark matter barely interacts with anything, even its own kind. It draws, and is drawn to all matter, but does not clump. It is exotic and very abundant by all accounts.
  5. Jan 9, 2010 #4
    Hi, thanx but I think it is subject to the same gravity as any other kind of matter. In that case why doesn't it clump? For what physical mechanism in particular?
  6. Jan 9, 2010 #5


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    There are various models of DM and DE that might produce a gravitationally bound collapsed body, such as Chaplygin dark star.

  7. Jan 9, 2010 #6
    It's more a case of lack of physical mechanism. One way to think about it is the earth, you have gravity holding it together but you also have quantum mechanical forces and electromagnetism keeping it apart. If you didn't have those other forces, the earth would "fall through itself". The matter would fall to the center of the earth, but once to moves through the center there would be nothing stopping it so it would keep going through the other side, and so it wouldn't clump.

    One other way of thinking about it, is to try to imagine air clumping or light clumping.
  8. Jan 9, 2010 #7
    Hi, interesting what you say...Thanx. But wouldn't it be an instability anyway? oscillating at first but then stabilizing somehow due to the large number of particles, I'm thinking about an N-body simulation of point masses, don't they clump somehow? i'm thinking about Jeans instability, I think it's called... If you consider the argument for gravitational collapse, relativistically, I think the singularity theorems imply the formation of black hole even in this case, where in the arguments does dark matter differ from relativistic dust (pressureless)? Doesn't it form a closed trapped surface anyway? I find this topic very interesting, anyway I suppose we should know more about the interactions of DM, here I'm only assuming it simply interacts gravitationally, ignoring any complication
  9. Jan 9, 2010 #8
    Looking at the Jean's equations, I think the problem is that there is always going to be an instability and the system never creates a stable clump.

    I'm pretty sure that if you put enough dark matter in one place, you will get a black hole. The problem is how do you get enough dark matter in one place since it doesn't interact with anything.
  10. Jan 12, 2010 #9


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    I think the electrons would go up and form a sphere much bigger than earth. But I calculated this myself some years ago, so I may be mistaken.
  11. Mar 23, 2010 #10
    I have to dig this up, since I had a very similar thought as the topic starter. One thing on which I feel that a detail hasn't been thoroughly discussed/answered however is (for me at least): Does DM interact with gravity at all, just a bit, or not at all?
    Or maybe more importantly: Has there been any evidence or observation supporting/excluding any of these options?

    It always struck me a bit odd, that galaxies (often) seem to form within gravity potentials of DM, but that there so far hasn't been detected any really big clump of DM - at least to my knowledge.
    Also, if DM can be found on the perimeter of galaxies (as a suggested cause for the "odd" rotational speed of outer stars in a galaxy), why isn't it attracted by the galaxy? Rotation around it might explain that, but wouldn't that also introduce enough drag to the normal matter in the vicinity to make it rotate in the speed expected without DM again?
  12. Mar 24, 2010 #11
    Is this all just speculation and wishful thinking, or is there any widely accepted (or at least regarded) evidence for the scenarios you propose?

    If DM doesn't repel from ordinary matter, and is attracted by it - shouldn't we observe objects that cause considerably more gravitational effect than it should (based on it's size and composition)?
    If DM doesn't interact with itself, it also should orbit/oscillate around/through large objects, which should be detectable as well. Also, DM would be attracted by "normal" black holes, and shouldn't be allowed to exit anymore, effectively feeding the BH. Is there any BH that indicates that it is much too heavy for what it consumed, making a contribution from DM necessary?

    I too could think of a lot of scenarios and possibilities. What bothers me is, which are in line with observations, likely/possible in some of the grander theories or even some definite word on this.

    Let me rephrase: Is there anything (any behavior) that we know about DM that goes beyond "it makes gravity"? How does it move, how is it distributed? Is there some basic principle to where lots of DM are? How does it, if at all, interact with its own kind?
    Or are these actually THE current questions astrophysics craves to find an answer to, too, but without anything concrete to say about so far?
  13. Mar 24, 2010 #12
    Here is an article from the current issue of Physorg ... it describes how we have been missing up to 90% of the universe because we have been looking using the wrong wavelength.


    What does this mean for Dark Matter .... it may be a coincidence that we have been missing 90% of creation and dark matter is supposed to make up a goodly percentage of that - but it is worth investigating.

    Does it call into question the very existence of dark matter?

    Does anyone know more about this?
  14. Mar 24, 2010 #13

    A theoretical problem with dark matter composite black holes is that the dark matter would evaporate via hawking radiation, which is a thermodynamic phenomenon composed of leptonic, baryonic and bosonic radiation, all physical properties not known to dark matter.
  15. Mar 25, 2010 #14
    One candidate for dark matter is the neutralino which is it's own antiparticle and will annihilate if they come in close contact with one another, producing high energy gamma-rays. If the black hole is large enough, this would take place within the event horizon, too small and the dark matter would annihilate before entering the BH.

    Last edited: Mar 25, 2010
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