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B How exactly do SMBHs in the center of galaxies form

  1. Feb 8, 2016 #1
    I've been thinking for awhile now, and I still don't understand how these types of black holes form, since they can't form by conventional means.
     
  2. jcsd
  3. Feb 8, 2016 #2

    PeterDonis

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    Have you looked to see what hypotheses astronomers have come up with?

    What do you mean by "conventional means"?
     
  4. Feb 8, 2016 #3
    The most accepted explanation on how stellar black holes and SMBH that do not form in galactic center's.
     
  5. Feb 8, 2016 #4

    PeterDonis

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    Which is? If you claim that SMBH in galactic centers cannot form by this means, you should be able to state briefly what this means is.
     
  6. Feb 10, 2016 #5
    I might be a little tired... so, what do you mean by that?
     
  7. Feb 10, 2016 #6

    PeterDonis

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    You said:

    What did you mean by "conventional means", and why do you think SMBH's cannot form by those means? Just saying "whatever the current accepted explanation is" isn't enough, because you still have to explain why you think the "current accepted explanation" can't explain the formation of SMBH's.
     
  8. Feb 10, 2016 #7
    What I meant was this; If we figure out the most logical way black holes form that would be the most regular way that they can form, but that means the SMBH's form either differently or undergo changes that stellar black holes don't undergo. But my thing is with those the exist in galactic cores. The way that all known galaxies are shaped suggests a massive orbital plane, and I also think that SMBH's in galactic cores have a less intense gravity well than that of other SMBH's and maybe even some strong stellar black holes, and that the size of the orbital plane has a lot to do with this. But I'm wondering what happens to these black holes that make them behave in such a way. Is it just that these black holes are a different type of SMBH, or is it that something changed them, making them the way they are, rather than just forming differently at the start.
     
  9. Feb 10, 2016 #8

    Chronos

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    It's a bit of a chicken and egg thing. SMBH and galaxies appear to have a symibiotic relationship. The bigger question may be how did billion+ solar mass black holes form so rapidly in the high zy universe. It's almost to the point it appears they must have formed around the time the first stars appeared, which is clearly a problem for the case of the hierarchical hypothesis - where SMBH essentially form through mergers of stellar mass black holes. One of the more popular ways around the problems of SMBH forming in the high z universe is the direct collapse model - where SMBH are formed by the collapse of huge primordial gas clouds directly into black holes. This sidesteps the furious merger rates necessary under the hierarchical model. For further discussion, see; http //arxiv.org/abs/1402.5675, The brief era of direct collapse black hole formation, and; http://arxiv.org/abs/1407.4472, The Direct Collapse of a Massive Black Hole Seed Under the Influence of an Anisotropic Lyman-Werner, and http://arxiv.org/abs/1411.5683, Direct formation of supermassive black holes in metal-enriched gas at the heart of high-redshift galaxy mergers.
     
  10. Feb 10, 2016 #9

    PeterDonis

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    In other words, you don't know whether or not SMBH's can or can't form by "conventional means". You're asking whether the mechanisms that form, say, stellar mass BHs are the same as the mechanisms that form SMBH's. The answer to that is, most likely not. But it would have saved time if you had asked that question directly in your OP, since that's the question you appear to be interested in.

    Why do you think that? (Hint: it's not correct.)
     
  11. Feb 11, 2016 #10
    Black holes usually consume most of the matter around it, if that was the case then I would assume that the galactic core would have a lot less matter, but it appears to me that is not the case. I think that the black hole is more spread out, affecting a larger area and therefore not having the same intensity as more compact ones.
     
  12. Feb 11, 2016 #11

    PeterDonis

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    Why do you think that? (Do you notice a pattern here? You keep on making flat statements which are, in fact, incorrect. You might want to take a step back and think about where you are getting these incorrect ideas from.)

    A black hole with a larger mass will be better at accreting matter than a smaller one, because it is larger. A larger hole is certainly not "more spread out" in the sense of having weaker gravity; it will have stronger gravity, because it is more massive. (It will have weaker tidal forces at its horizon, but that's a different thing, not relevant to this discussion.)

    But "larger" is still relative; in absolute terms, black holes are very small compared to other objects of the same mass. For example, the hole at the center of the Milky Way is thought to have a mass a few million times that of the Sun. That means its Schwarzschild radius is a few million kilometers--or only a few times the radius of the actual Sun. If that same hole were where the Sun is now, the planets would go around in their orbits much faster than they do now, but they could still be in stable orbits quite easily--they wouldn't just fall into the hole.
     
  13. Feb 11, 2016 #12

    Ibix

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    You are trying to reason from very vague non-numeric descriptions, which is what's leading to the errors Peter points out. Think about this: a black hole with a mass of a few million suns can be surrounded by just less than a few million suns and still be said to have consumed most of the mass around it. Since you haven't specified how big the volume "around" the black hole is, and you don't know how many stars you expect to be left (only that it's less than a few million) you don't have any way to say whether there are more stars "around" the black hole at the galactic core than you expect. This is why you always need to find numbers and maths before you try to make predictions, I'm afraid.
     
  14. Feb 11, 2016 #13
    I don't know how to explain what I'm trying to say without using my own drawing's. I don't have a broad enough vocabulary to just say what I mean. So me trying to explain what I mean is a futile endeavor, because everything you say is correct, but what I say doesn't come out properly enough. I know their are many steps before the action I'm trying to explain takes place, but I don't know the math and vocabulary to just describe it in words. If I did just say it, I would sound like an insane moron. So, I'll see if I can do something about that.
     
  15. Feb 11, 2016 #14
    Okay, I've tried, and it's not working, so instead of me trying to explain this, can someone else describe the causes that link every known galaxy to a SMBH and why these black holes are different from stellar ones, other than the obvious fact that they are more powerful.
     
  16. Feb 11, 2016 #15

    PeterDonis

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    We don't know that every known galaxy has a SMBH at its center.

    You're still assuming that SMBH's are somehow "different" from stellar ones in some respect other than having a larger mass. They aren't. So your question is based on a false assumption; that's why you're having so much trouble stating it in a way that will get an answer.
     
  17. Feb 11, 2016 #16

    PeterDonis

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    Why don't you take a step back and give us a reference to wherever you got the original idea that lead to this line of thought?
     
  18. Feb 12, 2016 #17
    Chronos already mentioned the direct collapse model.
     
  19. Feb 12, 2016 #18
    I think the problem here is that you know how stellar mass black holes can form as a result of a very large star collapsing.
    Yet supermassive black holes cannot possibly be produced that way, since the idea of a progenitor star having a mass of several millions times the mass of the Sun is absurd.
    This leaves two reasonable possibilities:
    1. SMBH are the result of solar mass black holes merging.
    2. SMBH results from the direct collapse of a very large volume of matter, the are no intermediate stages (stars).

    My personal preference is the second of these, but that isn't based on any actual data.
    I guess it's also possible that BOTH of the above might be the case - a very large volume collapsing which already has stellar mass black holes within it.
     
    Last edited: Feb 12, 2016
  20. Feb 13, 2016 #19

    Chronos

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    LIGO has the potential for detecting direct collapse black holes. They should produce gravitational waves of measurable strength.
     
  21. Feb 13, 2016 #20

    PeterDonis

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    I think there is actually a third possibility: a tightly bound system of stars like a globular cluster or a small galaxy (or a cluster at the core of a larger galaxy) contracts (as interactions between the stars gradually eject stars that are less tightly bound to the cluster and leave behind stars that are more tightly bound) to the point where stars in the center start to merge with each other and form a black hole, which then gradually swallows the rest of the cluster. This is sort of like your #2, but it still has stars as an intermediate stage.
     
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