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Old and distant clusters

  1. Aug 10, 2010 #1

    AWA

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  2. jcsd
  3. Aug 10, 2010 #2
    From my understanding, red stars are not necessarily old stars rather those coming towards the end of their lives. As high mass stars burn quicker, then I would suggest that this galaxy cluster is comprised of stars with a higher average mass than would be found in the present universe, (probably due to the higher density of gas at the time) hence they are burning quicker and appear redder.

    Thats just how I'd explain it :s
     
  4. Aug 10, 2010 #3

    AWA

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    Yeah, but I meant something plausible as an explanation. Stars in the main sequence don't appear redder because of "burning quicker", but due to the low relative temperature that in general is related to precisely the opposite, they are burning slower, due mainly to their low mass, but this is very basic kind of astrophysics 101, so I guess you were trying to kid about it.
    I'm interested in a more serious answer, but thanks anyway.
     
  5. Aug 11, 2010 #4

    Chronos

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    Old galaxies at high redshift are a common problem for modern astrophysics. We know they are 'old' because of high metallicity in their spectrums. The consensus view is that at least some galaxies evolved more rapidly than expected [for reasons not entirely clear] in the early universe. It is a mystery because we are fairly confident of our estimates of the age of the universe. I think this can, at least in part, be explained by the abundance of population III stars in the early universe.
     
    Last edited: Aug 11, 2010
  6. Aug 11, 2010 #5

    Chalnoth

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    Personally, I think that ultimately these issues will be resolved with a better understanding of dark matter (which significantly impacts early structure formation), and through more accurate simulations of early galaxies (simulations of galaxy formation are exceedingly difficult to perform).

    The second point is the most likely to change our understanding of early galaxy formation, aided by more and better observations of early galaxies.
     
  7. Aug 11, 2010 #6

    AWA

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    Population III stars have low metallicity, so how would they explain the high metallicity of this old cluster?

    Yes, but I sometimes see these tight estimates as a little drawback of the model. To have all the parameters(dark matter, dark energy, baryonic matter, flatness, age...) so highly constrained (finely tuned) make it appealing on one hand (precision cosmology) and very sensitive to discordant observations such as finding old galaxies with ever higher redshift pushing back the age) on the other, because if one changes one parameter, the rest has to change too.

    Sure, it's just that we are tightly constrained by the concordance model and by observation of high redshift galaxies when it comes to make simulations of early structure formation.

    I guess pretty soon we'll have observational evidence to know if the model stands as it is or some corrections need to be made.
     
  8. Aug 11, 2010 #7

    Chalnoth

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    I don't think that this sort of data will have much to say on the matter for some time yet. The main issue here is that doing the simulations of early structure formation correctly is computationally exceedingly difficult to get right, even if you know the underlying physics perfectly. We are forced to use a number of approximations to the underlying physics, and it's sometimes difficult to know just how much our approximations impact the final result of the simulation.

    For the time being, the primary way in which we will learn more about underlying physics will be by looking in areas that are largely unaffected by the vagaries of baryonic physics, such as structure formation on large scales. When we learn more about how galaxies form, then we may start to use them to probe underlying physics. For the time being, I would remain exceedingly skeptical of any claims of new physics that base their observational evidence on something as uncertain as galaxy formation simulations.
     
  9. Aug 11, 2010 #8

    Ich

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    ...especially as the authors themselves claim no such thing. From their paper, I'd say that they even don't see a real clash with the model they use for galaxy formation.
     
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