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How do black holes get so massive

  1. Nov 20, 2015 #1

    wolram

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    http://www.space.com/28664-monster-black-hole-largest-brightest-ever.html

    Astronomers have discovered the largest and most luminous black hole ever seen — an ancient monster with a mass about 12 billion times that of the sun — that dates back to when the universe was less than 1 billion years old.


    I dare say some one has an explanation of how these things get so massive, but they must stretch the powers of explanation and imagination.
     
  2. jcsd
  3. Nov 20, 2015 #2
    It's possible that it's always been, primordial black holes collapsed directly in over dense regions of the universe moments after gravity separated from the other forces. Remember that the universe was fairly dense (at least compared to now) early on, so black holes would have had a lot more stuff to feast on nearby.
     
  4. Nov 20, 2015 #3

    wolram

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    It is mind boggling, how many of these monsters are expected to be found.
     
  5. Nov 20, 2015 #4
    Primordial black holes could be everywhere, but the small ones would have evaporated by now and I don' think it'd be very possible for huge ones to exist without a galaxy around them. They would draw in matter the same as everything else and sink to the middle, some quasars probably started as primordial black holes. I don't see how a huge black hole can exist in intergalactic space for billions of years without finding it's way to the center of a galaxy, but I don't know.
     
  6. Nov 20, 2015 #5

    phinds

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    These two statements seem to be at odds with each other in that the first one says SMBHs might be primordial and the second one says they have to have galaxies around them (implying, I think, that they got to be super massive by feeding on the [non-primordial] galaxies around them).

    Did you mean this some other way?
     
  7. Nov 20, 2015 #6

    Chalnoth

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    Black holes really aren't as powerful (in terms of their gravity) as you seem to think. SMBH's are usually much less than a percent of the total mass of the normal matter in the galaxy. For example, Sagittarius A*, the SMBH at the center of our own galaxy, is about 4 million solar masses, while the total mass of all stars in our galaxy is roughly 50 billion solar masses, making our SMBH a mere 0.01% of the total mass of the stars in our galaxy.

    In short, galaxies do not form around SMBH's. SMBH's grow at the center of galaxies.
     
  8. Nov 20, 2015 #7

    Chalnoth

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    It is very difficult to simulate the behavior of matter in such extreme cases, so a lot of uncertainty remains. Very large black holes must grow from very large and dense clouds of gas. The Wikipedia page has some good information:
    https://en.wikipedia.org/wiki/Supermassive_black_hole#Formation

    One of the main difficulties with understanding how the largest supermassive black holes form is that when a black hole starts accreting matter rapidly, it gets extremely bright (it becomes a quasar/AGN). So bright, in fact, that it blows away any nearby gas. I believe it's currently unknown how the largest black holes can continue to accrete so much gas and grow so large.
     
  9. Nov 20, 2015 #8
    Yes, I'm aware of that, but I'm talking about the early universe (first few million years.) The amount of stuff in the universe may have significantly out weighed the black holes, but considering they were the only real objects until stars formed, wouldn't they have had the cosmic equivalent of an all you can eat buffet?

    I was speaking about different times, I'm saying that SMBHs probably came from primordial black holes. In a universe of just primordial black holes and gas, black holes would have eaten everything they came near, allowing them to grow out of control? The gas clouds may have outweighed black holes by thousands of times, but wouldn't that cause the black holes to be drawn towards the largest and most dense regions of space? Imagine a huge cloud of gas and thousands of tiny black holes roaming around, I'd imagine the cloud would draw in the black holes, and eventually, they'd settle all together at the core (dense objects always sink to the center.)

    What I said about SMBHs not existing without a galaxy around them doesn't imply that the galaxy was formed around the black hole, I was suggesting the opposite, that the black holes got drawn into the middle of galaxies.

    I would hypothesize that the early structure of the universe was dominated by huge gas clouds with huge numbers of small primordial black holes rapidly orbiting each other like a super heavy, dark globular cluster fully of black holes. A single black hole would eventually just eat everything near it and stop growing, but a cluster would throw some of them out into long orbits back into the gas clouds, allowing them to feed for much much longer. General relativity says that massive orbiting objects will slowly come together by leaking energy in the form of gravitational waves, so the clusters would form the monsters that we see today. Am I right?
     
    Last edited: Nov 20, 2015
  10. Nov 20, 2015 #9

    phinds

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    I have not idea if that comports with any existing theory but it sounds like a reasonable, and interesting, idea to me. I had always thought that "primordial BHs" meant tiny one, but that's based purely on ignorance and a possible misunderstanding/misinterpretation of what I have read.
     
  11. Nov 20, 2015 #10

    Chalnoth

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    Not really. Only matter that happened to get close to the black hole would be impacted.

    Given that primordial black holes themselves are highly speculative, no, they probably didn't form from primordial black holes.

    You need some form of friction for an object of any mass to sink to the center. This will work, say, if a SMBH is currently orbiting within a dense gas cloud. But not if the black hole is not within the gas cloud to start.

    But the very early universe was, to a very good approximation, mostly uniform with sound waves. I just don't think there would have been time for intermediate mass or supermassive black holes (if any existed at the time) to move very far from where they started.
     
  12. Nov 20, 2015 #11
    I thought during the very early stages of the universe, it was full of incredibly dense gas, more than enough to cause friction? Again, I'm not speculating that there were any SMBHs in the earliest stages of the universe, I'm saying they'd likely start out as hundreds or thousands of them of varying sizes. Why would they have to start within a gas cloud? If the gas clouds seriously outweighed the black holes, wouldn't the gravity of the cloud itself draw the black holes in? From there the friction with the gas itself would case them to sink towards the middle. Furthermore, when objects orbit in a vacuum, don't they slowly draw each other in by losing energy in the form of gravitational waves (which I know haven't been detected, but come out of the mathematics?) There should have been plenty of time for the larger primordial black holes to find their way into the biggest gas clouds, small ones would evaporate quickly, but planet or star sized ones should live for millions of of years.
     
  13. Nov 20, 2015 #12

    Chalnoth

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    It still takes time for a dense object to settle due to friction. I just don't think that SMBH's that didn't start near large overdensities will have the time to migrate to a large overdensity.
     
  14. Nov 21, 2015 #13

    wolram

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    From Wiki:

    The origin of supermassive black holes remains an open field of research. Astrophysicists agree that once a black hole is in place in the center of a galaxy, it can grow by accretion of matter and by merging with other black holes. There are, however, several hypotheses for the formation mechanisms and initial masses of the progenitors, or "seeds", of supermassive black holes. The most obvious hypothesis is that the seeds are black holes of tens or perhaps hundreds of solar masses that are left behind by the explosions of massive stars and grow byaccretion of matter. Another model involves a large gas cloud in the period before the first stars formed collapsing into a “quasi-star” and then a black hole of initially only around ~20 M☉, and then rapidly accreting to become relatively quickly an intermediate-mass black hole, and possibly a SMBH if the accretion-rate is not quenched at higher masses.[7] The initial “quasi-star” would become unstable to radial perturbations because of electron-positron pair production in its core, and may collapse directly into a black hole without a supernovaexplosion, which would eject most of its mass and prevent it from leaving a black hole as a remnant.

    210px-Artist%E2%80%99s_impression_of_the_huge_outflow_ejected_from_the_quasar_SDSS_J1106%2B1939.jpg
    Artist's impression of the huge outflow ejected from the quasar SDSS J1106+1939[8]
    210px-Artist%E2%80%99s_illustration_of_galaxy_with_jets_from_a_supermassive_black_hole.jpg
    Artist's illustration of galaxy with jets from a supermassive black hole.[9]
    Yet another model[10] involves a dense stellar cluster undergoing core-collapse as the negative heat capacity of the system drives the velocity dispersion in the core to relativistic speeds. Finally, primordial black holes may have been produced directly from external pressure in the first moments after the Big Bang. Formation of black holes from the deaths of the first stars has been extensively studied and corroborated by observations. The other models for black hole formation listed above are theoretical

    From what i make of this the most likely way for a BH to form is from pre existing stars. one thing i did not know and that is that BHs have the density of water, any way this seems a huge mass to form so early in our universes life time.
     
  15. Nov 22, 2015 #14

    Chronos

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    Current evidence tends to favor the idea that SMBH seeds have primordial origins. Accounting for growth of ordinary stellar mass black holes to SMBH sizes in less than a billion years remains an unsolved mystery.
     
  16. Nov 25, 2015 #15
    Is there any evidence of black holes in intergalactic space? Which we could, I guess, observe thru gravitational lensing effects “between” galaxies. I can’t seem to find anything on this on the Internet.

    If we do, wouldn’t this be evidence for the existence of those primordial black holes? I mean, if they formed in dense region in the super-early universe, one could argue that they just appeared in random patterns so that they should be dispersed everywhere. Now, unless they were an agents of aggregation for galaxy formation, which would make them present only in galaxies as they would have been a form of precursor (I guess), which seems to have been disputed above (“In short, galaxies do not form around SMBH's. SMBH's grow at the center of galaxies.“ post #6), we would get to see them in intergalactic space which is basically most of our universe's space.

    Would such evidence prove the existence of PBHs? Would evidence that there is no such black holes provide evidence that (1) PBHs do not exist or (2) PBHs are in fact the SMBHs at the center of galaxies?
     
  17. Nov 25, 2015 #16

    Chalnoth

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    I don't think there's any such evidence. As far as I know, the only evidence for black holes other than galactic nuclei that we have is from black holes in binary systems (where the black hole is in mutual orbit with a star). I just don't think it would be possible to detect the gravitational lensing around such a black hole.
     
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