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Black holes or galaxies first

  1. Sep 25, 2014 #1

    wolram

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    I am sure this question must have been dealt with before but i can not find an answer:

    What came first galaxies or black holes? How did supper massive black holes become so massive?

    List of most massive black holes

    http://en.wikipedia.org/wiki/List_of_most_massive_black_holes
     
    Last edited: Sep 25, 2014
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  3. Sep 25, 2014 #2

    phinds

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    I think that's an open question but with the consensus leaning towards the BH forming first and being key to the formation of the galaxies. Although I'm just parroting what I've read, it makes sense to me that way because if the galaxy forms first, there seems to be no way for a super massive BH to form whereas if the BH forms, there could then be a mechanism for the galaxy formation that would follow pretty logically. Also, if the galaxies form first, I can't see any reason why they would ALWAYS spawn a BH, whereas it now appears that there ARE BH's at the center of all galaxies, which you would expect if the BHs are key to galactic formation.

    My conclusion IS speculation on my part, though, and I know that my "common sense" and "logic" is often worse than useless when it comes to both QM and cosmology.
     
  4. Sep 25, 2014 #3

    Chronos

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    Agreed with phinds. The answer is currently unclear, but, the BH first option is fairly popular among scientists. It suffers some tension with the hierarchical model of galaxy formation, but, not unreasonably so. See http://arxiv.org/abs/1202.3848, Primordial seeds of supermassive black holes, for discussion.
     
    Last edited: Sep 25, 2014
  5. Sep 25, 2014 #4

    Vanadium 50

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    I don't think anyone knows for sure (and how could they?) but the thinking is that it's BH's first.

    A better way to ask this question is whether galaxy formation is driven by large scale fluctuations (galaxies first) or small scale (black holes first). For a long time we didn't know whether we had one or the other, or both. We know now that it's both, and they are of approximately equal strength. This favors small scales for two reasons. One is simply time. If you have a fluctuation that's 100 light years away/across, it takes 100 years for it to affect you. If it's 100 million light years away/across it takes 100 million years. Additionally, you can't have galaxies before you have stars, but you can have black holes even when you still only have gas clouds.
     
    Last edited: Sep 26, 2014
  6. Sep 26, 2014 #5

    CKH

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    Isn't this view of BH's forming first fairly recent and forced by the discovery of large BH's less than a billion years post BB? Before that, I think the accretion model within host galaxies was favored, but that theory has run out of time with the discovery of early supermassive BH's.

    Can the theory and measurements of the CMB deliver large enough density fluctuations on small enough scales to permit early supermassive BH formation? I was under the impression that the fluctuations diminish with size. Perhaps very small, local over densities are adequate?
     
  7. Sep 27, 2014 #6

    phinds

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    I don't know, but it has been my impression that the rationale is much more the fact that apparently ALL galaxies have supermassive BHs at their center. That can't be an accident for galactic formation, it has to be involved in the galaxy formation.

    good question. no idea.
     
  8. Sep 27, 2014 #7

    Vanadium 50

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    Phinds, you keep saying ALWAYS and ALL. I think that's a bit strong. There are certainly dwarf irregular galaxies that appear not to have them. One could say, "yes, but those aren't real galaxies", but that's kind of a No True Scotsman argument. Perhaps more relevantly, M33, which is a nice nearby spiral, has no supermassive black hole in its center.

    Also, even if every galaxy did have a central black hole, it wouldn't mean that this was a property of galactic formation. It could be a property of galactic evolution. We're pretty sure all galaxies have planets, and we're also pretty sure they are not the trigger for galactic formation.
     
  9. Sep 27, 2014 #8

    phinds

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    Yeah, I have to agree, I did overstate the case a bit.

    Certainly a possibility. That's really what this thread is about ... which came first the chicken or the egg. This at least seems likely to be one of those mysteries that WILL be solved someday. Maybe in our lifetimes?
     
  10. Sep 27, 2014 #9

    Chronos

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    While it is true not all large galaxies have an SMBH, it is unclear if they never had an SMBH, or kicked it out at some point. See http://arxiv.org/abs/1405.2072, Missing black holes in brightest cluster galaxies as evidence for the occurrence of superkicks in nature, for discussion.
     
  11. Sep 27, 2014 #10

    CKH

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    It would be interesting if the relationship is actually much tighter. Our galaxy is fairly large but the BH mass is only about 10^6 Mo. This is dwarfed by BHs in some galaxies that have masses of 10^9 Mo. I believe that some of earliest black holes discovered have masses in that range. I'm not sure how they measure the masses of such distant BHs. Does anyone know?
     
  12. Sep 27, 2014 #11

    Vanadium 50

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    The mass of central black holes is determined from the velocities of nearby stars.

    There is a strong correlation between the size of the central black hole and the size of the bulge. Triangulum has either no bulge, or a very small one. And no central black hole, or a very small one. (Small like 10^3 solar masses)
     
  13. Sep 27, 2014 #12

    CKH

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    So do you think that for very high redshift black holes (quasars), the bulge is imaged to estimate the mass? I'm wondering if some even more indirect method is used.
     
  14. Sep 27, 2014 #13

    Vanadium 50

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    I'm not an expert in QSO's but I doubt individual stars in even 3C273's host galaxy are measureable.
     
  15. Sep 28, 2014 #14

    Chronos

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    The size of QSO is inferred from their intrinsic variability. Some change so rapidly they cannot be much more than a light day in diameter.
     
  16. Sep 29, 2014 #15

    CKH

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    So the bigger the hole, the slower the variation, because the event horizon is large.
     
  17. Sep 29, 2014 #16

    Chronos

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    Quasar luminosity is believed to originate from an accretion disk, whose size is related to its distance from the black hole center of mass. The rate of change in brightness is constrained by the size of the accretion disk, which is larger than the event horizon for obvious reasons. So, the short answer is yes, a larger event horizon means slower change in luminosity. I prefer not to discuss it in terms of the event horizon because that implies the event horizon has some sort of objective reality, which is misleading. It is more like a rainbow - an illusion whose location is observer dependent. For discussion of quasar size measurement, see http://arxiv.org/abs/1201.3187, A Robust Determination of the size of quasar accretion disks using gravitational microlensing.
     
    Last edited: Sep 29, 2014
  18. Oct 2, 2014 #17

    wolram

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    One thing i do not understand is what is;

    the collapse of primordial density fluctuations
     
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