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Thread: galaxies

  1. #1
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    galaxies

    According to current cosmological theory. How long after the big bang should the first galaxy be formed.
    The moment an instant lasted forever, we were destined for the leading edge of eternity.

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    It is not well known. Large scale structure forms pretty early and in line with simulations, but the formation of small scales structure such a galaxies is a much more complicated process that is still not well understood. There are at least two main proposed mechanisms and the answer is dependent on how much each one contributes to galaxy formation.

    Observations indicate that galaxies were forming about 400 million years after the earliest point we believe we have good models for, which is quicker than expected but still feasible within the current theories.

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    Quote Originally Posted by Shaula View Post
    It is not well known. Large scale structure forms pretty early and in line with simulations, but the formation of small scales structure such a galaxies is a much more complicated process that is still not well understood. There are at least two main proposed mechanisms and the answer is dependent on how much each one contributes to galaxy formation.

    Observations indicate that galaxies were forming about 400 million years after the earliest point we believe we have good models for, which is quicker than expected but still feasible within the current theories.
    Would the good models predict galaxies at 800 million years after the big bang, or how long on average?
    The moment an instant lasted forever, we were destined for the leading edge of eternity.

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    Quote Originally Posted by Copernicus View Post
    Would the good models predict galaxies at 800 million years after the big bang, or how long on average?
    Sorry, that may have been misleading. When I said "the earliest point we believe we have good models for" I was referring to what you've called the big bang. I have rather come to dislike the term because there isn't actually such a point in current theory and people assign too much importance to it when you mention it.

    As I said we have a couple of main competing mechanisms. And the details of how things happen within them are complex. So "How long on average?" completely depends on how you tune your models. Somewhere between a couple of hundred million years and a billion. And we have observational evidence that the billion end of the spectrum is wrong.

    From memory about a decade back the simplest set of assumptions produced a prediction of about half a billion years - but we know that is wrong. At the moment we have pretty good models for the formation of large scale structure that mostly match what we see. Galaxies are much harder to model and there is a lot more we just don't yet know about how the process played out in detail. It's rather like the evolution of complex life - we have a good idea how when you are talking broad brush but the precise details about how individual species came about can be a little hazy.

  5. #5
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    There is no simple answer, today anyway.

    Certainly there were no galaxies like "today's" ellipticals until many a billion year had passed. Likely true of big spirals and lenticulars as well. If there were irregulars, they were likely not at all like what we see nearby today.

    AFAIK, the first observed "galaxies" look like clumps, barely a few hundred pc in size, quite unlike anything nearby today.

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