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On the rotation of black holes

  1. Jan 21, 2012 #1
    My question is this:

    Does the direction of spin of a supermassive black hole exert an affect on the spin of its surrounding galaxy (given that the above described black hole is at the center of such a galaxy)? Is there a direct or correlative effect? If so, can an in-depth explanation be provided?

    Example:
    The supermassive black hole at the center of the Milky Way galaxy spins clockwise. Therefore, the Milky Way spins clockwise. Is this true/false, and why?
     
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  3. Jan 21, 2012 #2

    DaveC426913

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    Well, it's not that a BH will exert a force on the galaxy, but they will both almost certainly rotate in the same direction since they both form from the same rotating mass.
     
  4. Jan 21, 2012 #3

    Chronos

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    That may be debatable, Dave. Supermassive black holes are generally thought to form via mergers, and there is no telling how that affects spin. In any case, I doubt black hole spin has much effect on galactic rotation. There may be local frame dragging effects, but, is probably not significant on galactic scales.
     
  5. Jan 21, 2012 #4

    DaveC426913

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    Perhaps, but a merger will certainly result in a spherical galaxy rather than a spiral, so its "spin" won't be a meaningful term - for a few jillion years at least.
     
  6. Jan 22, 2012 #5

    phinds

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    Is this an issue of whether the SMBH forms before the spiraling starts in what end up being a spiral galaxy or after? That is, it seems to me that if the SMBH form AFTER the galaxy is basically spinning [which I recognize at probably unlikely], it would almost have to develop the same spin, whereas if it formed from collisions in the still more amorphous galactic center, then the subsequent galactic formation might NOT be related to the spin of the SMBH. Does that make sense?

    Thanks
     
  7. Jan 24, 2012 #6
    i am an amateur at this stuff but, i believe that for a SMBH to form a very large body of mass larger than our sun needs to collapse inward. (ex. brown dwarf star) <--i think. so the body would already be spinning, thus the SMBH would acquire the same rotation at which it collapsed. (the mass' spin)
     
  8. Jan 24, 2012 #7

    DaveC426913

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    Perhaps, but that does not address the OP's question.
     
  9. Jan 25, 2012 #8
    This seems to be the most likely scenario.

    Correct me if I'm wrong but doesn't the primary theory for SMBH's involve one being at the center of all galaxies? That being said, it seems like they (SMBH's) would be the reason galaxies form where they do, not the other way around.

    It just doesn't feel right that galaxies (as we see them today) come before the SMBH. If that were the case I see no reason for a SMBH to be at the center of all galaxies instead of randomly distributed throughout the galaxy.
     
  10. Jan 25, 2012 #9

    Drakkith

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    Irish, I feel your view would be like saying the Sun was required to form before the gas cloud that collapsed to form the solar system in order for the gas cloud to collapse in the first place. I believe the galaxy as a whole (or rather its progenitor matter) began to collapse first, and the center of this collapsing cloud eventually formed the supermassive black hole.
     
  11. Jan 25, 2012 #10
    Heh okay when you put it like that my statement seems rather silly. On that note do galaxies need a SMBH at the center?
     
  12. Jan 25, 2012 #11

    phinds

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    Ah, that's a good question. Probably a Nobel prize in there if you can find the answer.

    They all SEEM to have them, but it's not proven that all do, nor is it understood why they should or what the formation processes are.
     
  13. Jan 25, 2012 #12

    Matterwave

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    A brown dwarf is a "star" much smaller than our Sun which is not massive enough to fuse protons via the proton-proton chain, but massive enough to fuse deuterium. They are usually ~12 Jupiter masses to something like .35 solar masses if I remember correctly.

    Because SMBH's are so much more massive than any star that we know of (some 10^8 or more solar masses), it doesn't seem plausible that such a massive "star" existed in the first place. SMBH's are almost certainly the result of many mergers of smaller black holes. How that can occur, given the dynamic time scales for galactic motion compared to the age of the universe, is not well understood. The universe doesn't seem to be old enough to have formed black holes of these sizes through "conventional" methods.
     
  14. Jan 25, 2012 #13

    PAllen

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    While a common theory is that supermassive black holes formed by accretion of dust and then stars into an initial black hole, there is no reason this is necessary. The total density of a SMBH is not particularly large (a billion star SMBH has a density measured at horizon of 1% that of water). One could imagine a central mass of a billion stars, slowed by dust, slowly coalescing to this density.
     
  15. Jan 26, 2012 #14

    Nabeshin

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    One can imagine, but I'm not sure this is physically realizable. What differentiates such a scenario from standard star formation (which obviously does not generate extraordinarily large black holes)?
     
  16. Jan 26, 2012 #15

    Chronos

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    I see no obvious reason galactic spin need align with that of its central SMBH. Even assuming the SMBH forms first, how does that dictate the spin of a galaxy that eventually spans hundreds of thousands of light years? I think the dark matter halo makes more sense.
     
  17. Jan 26, 2012 #16

    PAllen

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    It would have nothing to do with star formation. It would occur in well formed galaxies with large central star clusters. In fact, if a few stars happen to become black holes, I don't see how that changes the dynamics of the cluster. Once there is something (and it seems there must be) to allow sufficient exchange of angular momentum, it shouldn't matter whether you have stars or small black holes coalescing.

    Anyway, this is just a speculation; but so are all accounts of SMBH formation that I've read.
     
  18. Jan 26, 2012 #17

    Nabeshin

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    I see, sorry, I thought for some reason by your post that you meant direct collapse of a million solar mass cloud of gas into a SMBH (which I think we'll agree is impossible).
     
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