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Size of the first stars

  1. Jul 8, 2014 #1
    Looking at the huge clumps of higher elements (carbon silicon iron etc) present in our solar system, it seams as though only a few tens of billions of years would not be enough time to make all of the higher elements in the quantities we see today with stars like our sun that last billions of years.
    Were the majority of the first stars ultra large which lasted only millions of years?
    How soon after the big bang did these first stars form?
    Did the early (smaller) universe contain much larger stars that were much closer to each other (and much closer galaxies) that enabled the "sharing" of these newly formed higher elements?
    Would it be correct to think that most of these higher elements found on earth were formed in the first couple of billion years of the universe?
    Thanks for your help,
  2. jcsd
  3. Jul 8, 2014 #2


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    A large star 25 times as massive as the sun can spend as little as 6.4 million years on the main sequence, which is that portion in the life of a star where its energy comes from fusing hydrogen. At each stage beyond the main sequence (for example, burning helium, burning carbon, etc.), the duration of these stages is progressively shorter. The final stage of stellar evolution, just before core collapse, lasts only about 24 hours.


    There is evidence that the first stars could be truly massive in size, on the order of 100 solar masses, which would also imply a much shorter life before the formation of the supernova which destroyed those stars. The total lifespan of these massive stars would be but a brief instant compared to the current age of the universe.

    This article from Scientific American answers most of the questions you have about stellar formation and galactic evolution in the early life of the universe:

  4. Jul 9, 2014 #3
    In addition to SteamKing's response, early stars with very low metallicity generally need to burn hydrogen at a higher core temperature than younger, higher metallicity stars. This is because there will be very little carbon, nitrogen and oxygen for the CNO cycle, which is the dominant hydrogen forming nucleosynthesis process in massive stars and a small process in lower mass stars. Oddly enough then, early stars will compress slightly more under gravity to achieve the higher temperature and therefore have smaller radii than their higher metallicity equivalents. So they may be more massive, but certainly not larger!

    But yeah, there were definitely more massive stars in the early universe than now because of their relatively short evolution times and the fact that star formation rates tend to decline over time. Initial mass functions imply that there are always more lower mass stars than massive stars (see for example Salpeter IMF as a start). As for sharing of elements, this is typically managed either by close binary systems with accretion or by star formation in a gas cloud that is polluted by the yields of previous stars, the latter being most important for the presence of metals in stars. I'm not sure whether there were more binary systems in the early universe or not.
  5. Jul 9, 2014 #4


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    The lack of metallicity in the early universe allowed stars to become much more massive than at present. By some estimates, stars as large as 1000 solar mass could have been formed. Such stars, called population III stars, would have been very short lived and quickly pollute the universe with 'metals'. They may have formed as early as 100 million years after the BB. Steamking's SA reference covers this nicely.
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