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Do black holes swallow dark matter?

  1. Aug 2, 2010 #1
    What do we know about black holes swallowing dark matter? Dark matter exhibits gravitational effects, right [lensing and keeping star orbital speeds about galactic centers rouighly independent of their distance from a galactic center]? So it seems black holes should consume both normal and dark matter.

    Are there any theoretical ways to detect the effects of dark matter when it's consumed by black holes?? Anyone seen any discussions or papers?? Thanks?
     
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  3. Aug 2, 2010 #2

    mathman

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    Anything that is consumed by a black hole will add to the mass, charge, and angular momentum. Otherwise there is nothing to to identify it. In particular, dark matter and normal matter cannot be distinguished after being consumed by a black hole.
     
  4. Aug 2, 2010 #3

    nicksauce

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    Not to mention that there is a minuscule amount of dark matter in the galactic centre, where black holes are "swallowing matter", compared to the amount of baryonic matter.
     
  5. Aug 3, 2010 #4

    Chalnoth

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    Yes. And more important than that, dark matter doesn't experience much of any friction. This means that even if some dark matter gets in the vicinity of a black hole, it tends to just blow on by. It has to actually strike the black hole to go into it (and black holes are pretty darned small for their mass, so hitting one is difficult).

    This is contrasted to normal matter which, through friction, enters an accretion disk around the black hole, a disk that slowly collapses into the black hole through loss of energy from friction.
     
  6. Aug 3, 2010 #5
    All valid points in the above posts....yet with dark matter making up such a large proportion of all matter seems like it could have an effect....maybe somehow we could observe effects.

    Chalnoth...interesting observation

    I'm guessing Hawkings work on radiation did not reflect any dark matter ingestion...but I wonder if it could be expanded/modified to do so.
     
  7. Aug 3, 2010 #6

    Chalnoth

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    The problem is that the dark matter, within the galaxy, is at a much lower density than the normal matter. Most of the dark matter is in a "halo" that surrounds the galaxy. This isn't to say it's more dense out there, it's just a statement that the normal matter collapses through friction to form the galaxy, while the dark matter more or less stays in its orbit at after it first becomes gravitationally bound to the galaxy.

    So no, I don't think there would be much of an observable effect.

    The closest thing to this suggestion that I've seen is that because of the fact that normal matter is so much more dense, it's going to attract some amount of dark matter to it. With more dark matter comes more annihilations (dark matter is expected to be made up of equal parts matter and anti-matter, because it must interact too weakly to have annihilated in the early universe to have the properties we observe). Dark matter annihilations are expected to be one observable signal we could potentially use to understand its properties.

    One attempt at observing annihilating dark matter comes from WMAP observations:
    http://arxiv.org/abs/0802.3830

    At this point, I would place this observation of the WMAP haze at speculative at best. But at least it serves as a model of how one might go about observing dark matter directly.

    I don't think it makes any difference whatsoever.
     
  8. Aug 3, 2010 #7
    Only when they are on a diet.

    :cool:
     
  9. Aug 4, 2010 #8
    This is a question for me. Dark matter would orbit the center of mass. But since it does not interact much it would just pass to the other side without interaction. I have to think, though, that there would still be a much greater density of DM at the center than at the edges simply because the gravitational field is stronger there. Sure it would be traveling faster, but there would be more of it. Perhaps there could be a greate enough density of DM to form a BH.
     
  10. Aug 4, 2010 #9

    Chalnoth

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    Yes, the density of dark matter is expected to be larger near the galactic center. Not enough to make the density outweigh the normal matter, but still larger than it is outside the galaxy (if we define the galaxy as the normal matter part). As far as I'm aware, however, our observations of dark matter are not yet accurate enough to confirm this. But it is definitely expected from theory.
     
  11. Aug 5, 2010 #10

    Chronos

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    Dark matter is not interactive with normal matter. It would pass right through a black hole. See the bullet cluster paper.
     
  12. Aug 5, 2010 #11

    Ich

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    Huh?
    Nothing passes right through a black hole.
     
  13. Aug 5, 2010 #12

    Vanadium 50

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    It gravitates (that's how we know it's there). It would therefore be captured by a BH in exactly the same way as normal matter.
     
  14. Aug 5, 2010 #13
    If we have already established that DM can develop pockets of larger density when before it was an even distribution, then the question is why can't it become even denser and form BHs made only of DM. If it can become dense to begin with, then what's to stop it from becoming even denser?
     
  15. Aug 5, 2010 #14

    Chalnoth

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    In principle it might, but the time scale for such a thing would be exceedingly long. The reasoning is as follows:

    1. To form a black hole, you need a local overdensity of dark matter so great that it prevents the dark matter from escaping. The magnitude of this overdensity is vastly above the typical average density of dark matter within a galaxy or galaxy cluster.

    2. In order to get such a massive overdensity, you need the orbits of the dark matter particles in a potential well to decay. This can only be done through friction.

    3. Dark matter experiences almost no friction.

    If you make the assumption of perfectly non-interacting dark matter, I'm sure you could calculate just how long this would take. Given our observations, this time scale must be many times the current age of the universe (because if it weren't, dark matter would have collapsed noticeably by now: it hasn't).

    However, this may well turn out not to work for real dark matter, because real dark matter is likely to have some interaction. In particular, it is likely to be nearly equal parts matter and anti-matter, meaning that any significant overdensity of dark matter will also be very efficient at causing the dark matter particles to annihilate, likely causing the structure to evaporate long before it gets dense enough to form a black hole.
     
  16. Aug 5, 2010 #15

    George Jones

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    When normal matter collapses, it loses energy through radiation, which tends to hasten collapse. Dark matter doesn't do this. Consequently: 1) normal matter forms black holes more easily; 2) black holes present larger effective targets to normal matter than they do to dark matter.

    A quote from Weinberg's new cosmology book:
    [EDIT]Chalnoth posted much the same stuf while I was composing my post.[/edit]
     
  17. Aug 5, 2010 #16

    Chalnoth

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    By the way, as a potential point of interest, even without any interactions (other than gravity), dark matter particle orbits will still decay over very long time scales. The argument goes as follows:

    1. From time to time, dark matter particles will have close interactions with other dark matter particles that exchange energy between them. This means that the particles of dark matter in a potential well will be thermalized: their energy distribution will approach a thermal distribution with time.

    2. A thermal distribution has a high-energy tail of particles that have enough velocity to escape the potential well. Thus the particles in the high-energy tail of the thermal distribution are always escaping. Since it is the highest-energy particles that escape, the average energy per particle is reduced in this process, meaning that it causes the cloud to collapse.

    I do not know if this effect or the (weak) non-gravitational dark matter interactions turn out to be the dominant effect in controlling the long time scale behavior of dark matter.
     
  18. Aug 8, 2010 #17

    Chronos

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  19. Aug 9, 2010 #18

    Chalnoth

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    Those headlines seem to be a bit misleading. The only thing that was found, as near as I can tell from reading the articles, is that the density of dark matter in the vicinity of black holes is not large enough to produce runaway accretion of dark matter into the black hole.
     
  20. Aug 10, 2010 #19

    Chronos

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    These studies assert dark matter comprises a miniscule amount of the mass of black holes. Quoting from page 6 of arXiv:0802.2041v1:

    " . . . We found that dark matter contributes to no more than 10% of the total mass accreted by black hole seeds."

    This is the conservative upper limit and suggests black holes tend not to absorb dark matter, hence the headlines.
     
  21. Aug 10, 2010 #20

    Ich

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    This is exactly what has been said in this thread: DM is less readily absorbed by black holes because it can't form accretion disks. It contradicts the claim that DM "would pass right through a black hole".
     
  22. Aug 11, 2010 #21

    Chronos

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    The dark matter component of black holes appears to be vanishingly small, or nonexistent. It may be that dark matter does not accrete and just slides by, or that it simply passes through black holes. The properties of dark matter are not understood, nor is it necessarily bound to our present understanding of the laws of physics.
     
  23. Aug 11, 2010 #22

    Ich

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    It is bound to gravitate. That's how we know about it.
    So no, it will not pass through a black hole. No way.
     
  24. Aug 11, 2010 #23
    If DM particles passed through BHs, then I think that would prove that it is not a particle at all subject to following the curvature of spacetime.
     
  25. Aug 11, 2010 #24

    Chalnoth

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    ...which would indicate that they couldn't cluster, which would be incompatible with our observations.
     
  26. Aug 13, 2010 #25
    Guessing is not science. Compare hypothesis to hypothesis, hypothesis to observations. Logic analysis (pros/cons of each hypothesis) as opposed to picking a hypothesis and force feeding the observations to the chosen hypothesis.

    It is a mistake to discard any reasonable hypothesis, however, if the "laws of physics" must be changed to make a hypothesis work that should be reason to consider other explanations.

    AGN and QSO Super Massive "Black holes" have a maximum mass of approx. 3 x 10^9 solar masses. (That is one of the observations that requires an explanation.)

    There is currently no explanation for the 3 x 10^9 solar mass BH limit observation. Galactic mergers in addition to dark matter would if "black holes" are classic black holes have created black holes in excess of 3 x 10^9 solar masses. (i.e. As noted because dark matter has not been detected and because there are observations such as the spiral galaxy rotation velocity variance with radius that is not in accordance with simulations that use the dark matter hypothesis, it possible that dark matter does not exist. Even if dark matter does not exist, normal matter would have created SMBHs in excess of 3 10^9 solar masses due to galaxy mergers based on statistical analysis of the number of mergers with time and the mass of SMBH merging.)

    Here are other related observations that might help to provide a guide to the solution. (Think about Disney's finding that spiral galaxy parameters (luminosity, rotation velocity, and mass) are controlled (non-random) which indicates there is a single unknown parameter/mechanism that is controlling the spiral galaxy.

    There is the problem of how to explain why spiral galaxies have not become elliptical galaxies due to mergers.

    There is evidence of bimodal emission of spiral galaxies. The bimodal emission mechanism appears to be related what causes star burst galaxies.

    We need a thread summarizing QSO observations.

    The QSO spectrum is non-thermal generated. There are peculiar QSO emission structures (i.e. What moves matter in peculiar locations around the QSO and what causes it to emit in those locations?). QSO emission shows unexplained long term (periodic variation continues throughout the observation period, 30 years) periodic variance. 10% of QSO are naked quasars, which have the narrow region emission, but do not exhibit broad line region (BLR) emission (BLR is believed to due to emission from an accretion disk). The point is the QSOs in question do not have an accretion disk and are by some other mechanism causing the narrow line emission.

    In the vicinity of our galaxy's SMBH there are peculiar paradox of youth stars. (Short lived very large stars located very close to galaxy's core.) These peculiar stars are OB very large stars which have peculiar orientations. (There are for example two strings of these supposedly OB stars in our galaxy that are orientated 90 degrees to each other with opposite rotations about the massive object at the center of our galaxy.)

    There is the Holmberg effect. Satellite dwarf galaxies that orbit our galaxy and other spiral galaxies are aligned 90 degrees to the plane of the spiral galaxy.

    There is the recent finding of Ultra Luminous x-ray sources in the vicinity of spiral galaxies's core.

    Galactic clusters have anomalously hot intergalactic gas that is emitting x-rays. (10^7 K, very, very large structures). There is no explanation as to what could heat the cluster intergalactic gas to such high temperatures and there is no explanation as to why the cluster intergalactic gas has not cooled. The cluster intergalactic gas mass is roughly the same as the mass of the cluster's galaxies' mass.

    http://arxiv.org/PS_cache/arxiv/pdf/1002/1002.0553v1.pdf

    http://arxiv.org/abs/astro-ph/0501312v1

     
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