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Direct collapse black holes

  1. Apr 2, 2015 #1

    Chronos

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    This paper http://arxiv.org/abs/1504.00263, Assessing inflow rates in atomic cooling halos: implications for direct collapse black holes, discusses formation of direct collapse black holes in the early universe. Supermassive black holes are the only reasonable explanation for quasers in the high z universe. A long standing question has been how can black holes achieve such staggering masses in such a short time after the BB? It is believed some SMBH could have been seeded via direct collapse, but, it has also been thought the UV background would suppress their numbers well below those necessary to explain high z quasar populations. The authors appear to have found this is not necessarily the case.
     
  2. jcsd
  3. Apr 7, 2015 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
     
  4. Apr 8, 2015 #3

    marcus

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    Chronos thanks for the pointer. The senior author Marta Volonteri is something of an expert specialized in Black Holes (massive and up). Good publication and citation track record. She got her PhD in 2003 and has over a hundred papers. She has co-authored with Joe Silk and other reputable people. Both authors are at Sorbonne and Paris CNRS Astrophysics. The paper seems to be based on numerical simulations of collapse under various conditions relevant to high z (early times). The junior author, Latif, may have been instrumental in the number-crunching. These are just random superficial observations but may help me see the paper in context. I think it could be important by steering people to a better understanding of how we got so many high-z quasars.
     
  5. Apr 8, 2015 #4

    Chronos

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    I was a little disappointed no one else found this interesting enough to comment on - tx marcus!
     
  6. Apr 19, 2015 #5
    As well as black holes, are not massive objects where the bulk of the matter exists in pre-collapse, in a relatively thin layer outside the Schwarzschild radius also candidates?
     
  7. Apr 19, 2015 #6

    PeterDonis

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    Such an object cannot be stable; it will quickly collapse into a black hole (more precisely, in the state you describe it must be in the process of doing so).
     
  8. Apr 19, 2015 #7
    Which? Do you have a reference for instability that leads from collapse to a black hole in some sort of quick manner?
     
  9. Apr 20, 2015 #8

    Chronos

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    Huh? What thin layer outside the Schwarzschild radius [of what?] are you talking about?
     
  10. Apr 20, 2015 #9

    Garth

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    Last edited by a moderator: May 7, 2017
  11. Apr 20, 2015 #10

    PeterDonis

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    It is impossible to have a stable equilibrium for any object with radius less than 9/8 of the Schwarzschild radius. Einstein proved this as a theorem in the 1930's. So any "thin layer close to the Schwarzschild radius" can't be stable; it must be in the process of collapsing.
     
  12. Apr 21, 2015 #11
    I'm not very familiar with the physics of the early universe. I'm not even sure what variables are calculated, but I'm curious about the "isolation" of gravity in the early universe.

    If matter (as we know it now) was created everywhere then wouldn't there be greater attraction "everywhere locally". As the sphere of influence enlarges with time the effect of surrounding mass would reduce the local attraction? Laymen's terms as you start to see more stars around you then they would start to "pull apart" your local spacetime. Or would symmetry just typically cancel it out?
     
  13. Apr 21, 2015 #12

    PeterDonis

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    Matter wasn't "created everywhere" in the sense of stress-energy, which is the source of gravity, suddenly appearing where there was none before. The SET is locally conserved: it can't be created or destroyed, it can only change form. At the end of inflation, the SET changed form from the "false vacuum" inflaton field to ordinary matter and energy; but the "amount of stress-energy" was the same before and after the conversion, so the source of gravity did not change.

    On average, the universe is homogeneous and isotropic, so the "effect of surrounding mass" on a given piece of matter is zero.

    Yes. See above.
     
  14. Apr 21, 2015 #13
    Well that all confirms what I thought, by the time I typed "cancel it out" I was tempted to delete the post.

    One last "stupid" thought, but from what I think I know if the universe was too smooth and evenly distributed galaxies wouldn't have formed. Some unexplained "balance" allows galaxies to form and group, yet loose enough to keep SMBHs from swallowing everything as this thread proposes was an evident epoch in the first billion years? I bet this is a bit "out there" but could constructive and destructive interference have an impact?
     
  15. Apr 21, 2015 #14

    Garth

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    Not a stupid thought at all, but an interesting and difficult question that cosmology tries to explain.

    The "balance" is provided by Inflation in the standard cosmological [itex]\Lambda[/itex]CDM model, which makes the universe smooth yet with sufficient anisotropies, as seen in the CMB, to create the large scale structure of the universe. It does, however, require sufficient Dark Matter to accelerate that process.

    Inflation and Dark Matter have not been discovered in 'laboratory experiments - but the LHC is having a good go at detecting something beyond the present particle physics standard model, as that model was completed by the discovery of the Higgs Boson.

    We wait and see!

    Garth
     
    Last edited: Apr 21, 2015
  16. Apr 21, 2015 #15

    Grinkle

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    This is not at all the point of the thread, but the sidebar on mass outside the SR reminded me that I don't understand how black holes of differing masses can be observed unless the mass we are observing is all still on the verge of crossing the SR, since nothing (I think) can cross the SR (or maybe I mean the event horizon) in a finite amount of time according to GR.

    Discussions I have seen on the topic tend to fall into two camps -

    Singularities do form in finite time, we don't have math to describe a singularity, that is why its called a singularity

    vs

    We are observing matter in the process of collapsing, the singularity itself will inevitably form, but not in finite time.

    At least that is how I summarize what I have read.

    If anyone can point me to a good discussion on the topic, I'd appreciate it. Its befuddled me for a long time.
     
  17. Apr 21, 2015 #16

    Chronos

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  18. Apr 21, 2015 #17

    PeterDonis

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    No, that's not what GR says. The problem is that statement "a finite amount of time". "Time" without qualification is not an invariant; it depends on your choice of coordinates. In Schwarzschild coordinates, yes, nothing reaches the horizon in a finite amount of coordinate time. But there are other coordinate charts in which objects do reach the horizon in a finite amount of coordinate time (for example, Painleve, Eddington-Finkelstein, or Kruskal).

    What GR actually says is that coordinates don't have physical meaning; the physics is contained in the invariants, the things that don't depend on your choice of coordinates. For example, we can compute the proper time for an object to free-fall to the horizon from some finite radius; this computation gives a finite answer. Proper time along a given worldline is an invariant, so the finite answer is telling us something with physical meaning: namely, that objects can fall to the horizon, and on through it to the interior of the black hole. Similar computations for an object like a star that undergoes gravitational collapse show that, to an observer riding along with the collapsing matter, a horizon forms in a finite proper time, and the matter continues on inward and reaches ##r = 0## in a slightly longer finite proper time, where it forms a singularity. Again, these computations are of invariants, so they have physical meaning: they tell us that collapsing matter can form a horizon.

    As for how we can observe holes of differing mass, even after the collapsing matter falls through the horizon, the reason is that the "mass" we observe is really an "imprint" on spacetime that is left behind by the matter even after it collapses. The way we measure the mass of a black hole, or any astronomical object, is to put test bodies in orbit about the object and measure the orbital parameters. What we are actually doing when we do this is measuring the spacetime curvature due to the object. But the curvature due to the collapsed object is static; once it forms, as the object collapses, it stays the same; the object does not need to be there continuously to produce it. (This is ultimately because the Schwarzschild spacetime geometry is a vacuum solution, i.e., no matter needs to be present to sustain it.) So the mass of the object is still measurable the same way even after it has collapsed to a black hole.

    I'm not sure I like this presentation of the issue; it says some things in a way that appears to me to invite misunderstanding. Also, at least one statement it makes is simply wrong: it says "the event horizon is part of future null infinity", which is not correct.
     
  19. Apr 21, 2015 #18
    I love the simulation approach. "Operational Dynamic Modeling" Of a sort. Enzo looks pretty amazing.

    So, some random fluctuation to start accretion is assumed already. Then for direct collapse you need the right balance of UV flux to warm the in falling mostly H1 gas, dissipate angular momentum, make it less likely to fragment, and keep it ionized (non-molecular) to inhibit fusion ignition? But the most important piece is mass accretion rate. How exotic are the rates they are estimating?

    They mention sink particles? Which I was a little confused by. These are protostars? So in the direct collapse fusion is inhibited but only part of the way down, and still you have a protostar (a really massive one, or just normal?) but then is that still going to be isothermal collapse? Are they saying a fairly massive protostar is there as usual but the density is low because it's from a primordial low metal cloud so the outward energy pressure is still low, or the outward pressure is normal for a massive protostar, but just gets overwhelmed by high mass in-flow? Total cartoon, but I guess I have hard time picturing the gravitational process (especially low density) blowing by the outward pressure from the protostar fusion ignition. I thought stellar fusion pressure was pretty effective at overwhelming the puny tug of gravity.
     
    Last edited: Apr 21, 2015
  20. Apr 21, 2015 #19
    I am simply asking for a formation calculation. A reference would be fine. In the case of spherical symmetry, how much cosmological time is required such that a mass m will find itself fully within a radius 2m?
     
  21. Apr 21, 2015 #20

    PeterDonis

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    What is "cosmological time"? If you mean proper time for an observer falling in with the collapsing matter, then for a star with the size and mass of the Sun, it takes about an hour to collapse to r = 2m. This was first calculated by Oppenheimer and Snyder in their classic paper on gravitational collapse in 1939. Misner, Thorne, and Wheeler has a good discussion.
     
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