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Dark Age: Galaxy & Quasar Formation ?

  1. Feb 27, 2004 #1
    This is my first post, so I am going to get straight into a double barreled question that has been bugging me for a while.

    (1) How long does it take for stars to conglomerate around a general loci, in order to form a proto-galaxy. ?

    I ask this in the light of the most recent Hubble images of a yet un-named galaxy cluster reported to be between 13 to 14 Billion years old. As of the moment, it happens to be the oldest known galaxy ever recorded.

    What troubles me and causes some confusion ( at least in my mind ) is this.

    Given the time between the Big Bang, ( BB ) the inflationary period and the so named "Dark Ages" before the first stars lit up is only about 800 to 900 million years. At least half if not two thirds of that period, the only matter that existed was mostly hydrogen and some helium.

    So it seems ( to me at least ) that proto~stars and proto~galaxies must have been forming during the so called dark ages or almost immediately afterwards.

    That probably will be easy for someone to explain to me.

    So we arrive to question (2).

    How is it that over a dozen Quasars have been discovered in connection to this extremely old proto~galaxy ?

    I am not clear if they were detected within the body of the galaxy or outside of it. Either way, they a reported to be the same age.

    No doubt someone will point out the error in my thinking, but I am troubled by the limited time~frame within which all of the above things could have occured.

    I say this because, I would have thought that more than a mere 300 to 500 million years** after the BB, would be needed for... (A) things as complex as galaxial structures to form and (B) for massive stars to have utterly exhausted their fuel ( remembering the prodigious amounts of raw material at hand at this early stage of the universe) before collapsing to form Quasars.

    I would appreciate some help on what truly baffles me.


    ** If my memory serves me correctly, that original period of 800 to 900 million years after the BB, included 500 million years of reionization when there was no matter heavier than hydrogen and helium, plus radiation.

    So the time period in question for all of the above things to have formed such complex structures or to have formed Quasars, narrows down to an even smaller slice of time. A band of probably not more than 350 to 400 million years.

    Is there something I am missing out here, or is there some sort of time measurement problem ?
    Last edited: Feb 27, 2004
  2. jcsd
  3. Feb 27, 2004 #2


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    Welcome to Physics Forums!

    Only have time for a quick response...hopefully someone else will be by soon.

    AFAIK, there is still a lot of uncertainty as to when the first stars and microgalaxies formed. Some recent articles I've seen place this as early as 100 to 200 million years after the BB. Often times, I see more generalized timeframes like "a few hundred million years after the BB". Perhaps your 800-900 million year timeframe is from older research? I'd have to look into it...
  4. Feb 27, 2004 #3


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    Some quick answers:
    - the first stars formed very quickly (<~100 million years), and it is thought they were very massive (~>100-1000 Msol)
    - they also became supernovae quickly, seeding nearby regions with heavy elements; they collapsed to form black holes
    - which came first - black holes or (proto-)galaxies? that's an open question right now
    - it seems the initial galaxies were quite small, ~1k light years
    - the Dark Ages are the time when the gas between clumps (stars, proto-galaxies) was neutral (or, more accurately, the hydrogen was not ionised); it took ~800 million years for the UV emitted by stars to ionise this gas
    Do you have a link to a report on this? It seems to be too short a summary for me to comment on.

    You may find "The First Stars in the Universe" article in Scientific American (December 2001) of interest.

    Things to keep in mind when reading some of the recent articles claiming that some observations don't fit the 'consensus model' (of cosmology):
    - HST, Chandra, XMM (and now Spitzer) observations are, for the most part, of a small number of objects; it will take many more observations before we can be sure that an early, massive galaxy cluster (for example) is typical or quite abnormal
    - sometimes an astronomer will rush into print before an observation has been fully analysed; while it's fully understandable behaviour (it's a pretty competitive environment, with more researchers than funding!), it can lead to quite misleading perspectives
    - cosmological models have made great strides in the last 10 years or so, and observations have advanced to the point where many models can now be seriously tested; however, it's still early days ... stay tuned, for the next exciting story in the saga of homo sap. and the universe!
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