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An Age Problem (again)?

  1. Jan 30, 2015 #1

    Garth

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    We have had:
    [/PLAIN] [Broken]
    Is there an Age Problem in the Mainstream Model? (Oct 2005)

    Cosmic age problem ? (Nov 2008)
    Is There An Age Problem In The Early LCDM Model? (Jun 2010)
    Massive galaxy cluster could upend theory of universe evolution, (Dec 2014)

    and now: SDSS J013127.34-032100.1: a candidate blazar with a 11 billion solar mass black hole at z=5.18. (Jan 2015)

    From that paper:
    The solution they propose is that if some of the accretion energy went into powering the jet then it did not contribute to the Eddington limitation on the accretion rate.

    Still the existence of this 'blazar', and the inference that there must be hundreds more, stretches the envelope limiting how massive an object can be that exists in the early universe.

    Note the Eddington limited accretion rate determines the maximum rate that an object can accrete, so the actual rates, and hence the sizes achievable at a set red shift, are going to be less than this limit.

    With the other objects described in the earlier threads it seems that the early universe contained some pretty large and evolved objects. As the red shift of observed objects keeps getting pushed back to earlier times it may be that a real age problem in the early universe of the standard LCDM may soon manifest itself.

    We wait and see....

    Garth
     
    Last edited by a moderator: May 7, 2017
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  3. Jan 30, 2015 #2

    mfb

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    This is probably a stupid question, but where did they rule out merging black holes as substantial growing process? I don't see how those mergers would be Eddington-limited, and I don't see a discussion of this in the paper.
     
  4. Jan 30, 2015 #3

    Garth

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    Hi mfb,

    No they don't discuss BH mergers and this is one way SMBH's are thought to have formed.

    However had there been enough time at t = 1.1 Gyr for a series of such mergers to have happened?

    For example, starting by direct collapse, in this paper Formation of supermassive black holes by direct collapse in pre-galactic haloes we read:
    Now the problem with our 'Blazar' is that the SMBH is not in the present universe but is seen at z = 5.18.

    So one would have to go from direct growth from 104 - 106 M by mergers to 1010 M i.e. requiring ~ >104 mergers between z ~ 6 and z ~ 5, that is between 0.942 Gyr and 1.135 Gyr (Ned Wright's calculator) after BB or in a period < 200 Myrs.

    Now there are many merger paths that could lead to that final mass at z =5.18, but you see the difficulty of the problem of building the SMBH in the time available.

    Garth
     
    Last edited: Jan 30, 2015
  5. Jan 30, 2015 #4

    mfb

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    Figure 4 suggests a roughly exponential growth along the Eddington limit. If we take the line ##\eta=0.3##, ##\eta_d=0.1## and start with 20 solar masses as seeds, then we need 500 black holes to merge. That does not have to happen sequentially, we just need 500 seeds eventually merging into one big black hole. I have no idea know how probable that is, however.

    The merger paper gives "ample time" for growth, so it could happen faster I guess.
     
  6. Jan 31, 2015 #5

    Garth

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    Yes, it is just possible to produce the 1010 M SMBH at z = 5.18 if you can start with a seed BH at z = 20 of 104 M.

    If the disc accretion efficiency, ηd, is high (quickly spinning) then the object is "super bright". To explain the "dimmer" observed luminosity the rate of mass accretion onto the BH, ηd, has to be lower and the BH would therefore grow at a slow rate, so it is difficult to explain large black hole masses at high redshifts.

    On the other hand, if a lot of the accretion energy goes into powering the jet then you can explain a high ηd with a lower luminosity while still yielding a high accrertion rate and large BH mass.

    But everything has to accrete at the fastest possible rates right up to the Eddington accretion limit.

    All we need now is a decent theory of how the accretion disc produces the jet!!

    My main point though is that we are continually discovering massive or highly evolved (high iron metallicity - 3 solar abundance at around z = 4) objects at high red shift. This is just the latest in a line of such difficult-to-explain objects.

    As observing techniques improve we are pushing out to higher and higher redshifts, (see the progress in the linked threads in my OP over the last 10 years) and one would have thought these objects would have dried up at such early times, however it seems that they haven't.

    Indeed in this last paper it says that because of selection effects (the blazar jet has to point towards us): "This implies that there must be other (hundreds) sources with the same black hole mass of SDSS J013127.34–032100.1, but whose jets are pointing away from Earth."

    So this very massive BH is not just some single outlier in a statistical distribution.

    We push on to even higher z, it will be interesting to see whether our explanatory power can keep up!

    Just a thought,
    Garth
     
    Last edited: Jan 31, 2015
  7. Jun 6, 2015 #6
    Worth mentioning that while cosmologists need to include black hole mergers in their models, not all astrophysicists are happy about releasing the necessary amount of angular momentum. And even cosmologists tend to agree that, for standard models to work, an awful lot has to happen in a mere 14 billion years.

    Nigel
     
  8. Jun 6, 2015 #7

    Garth

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    Hi Nigel,

    It's the awful lot that has to happen in first billion that's the problem!

    Garth
     
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