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Age of universe compared to age of sun.

  1. Mar 27, 2004 #1
    I'd be interested to hear people's comments.

    One thing especially. The current estimates are of the order of 20bn yrs and 5bn yrs respectively (the actual values are not important ... it's the 'order' of the ratio that interests me). So, our sun has been around for a quarter of the age of the universe. Just one insignificant star, in a insignificant galaxy, etc. etc.

    A related question would be to do with how many 'generations' of stars could there possibly have been since big bang? It can't be many. Are there really enough to have produced the distribution of elements as measured today?

    Another one would be about the expected lifespan of the universe itself. I assume that it's huge orders of magnitude larger than the lifespan of any 'typical' star, so surely that means that we must be living in the earliest stages of the life of the universe.

    Is any of this remarkable in any way?
     
    Last edited: Mar 27, 2004
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  3. Mar 27, 2004 #2

    Janus

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    One thing that has to be taken into account is the fact the stars responsible for the distribution of elements are stars that have supernovaed. These in turn must be stars that are were massive than our own. The more massive a star, the greater its luminousity, the faster it burns its fuel, and thus the shorter its life time. Really massive stars can have their lifetimes measured in the millions not billions of years. So literally thousands of "generations" of these larger stars could have been born and died since the beginning of the universe.
     
  4. Mar 27, 2004 #3

    Nereid

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    Several types of stars other than supernovae also produce and distribute newly created elements into the inter-stellar medium (ISM), to become future stars and planets. These include novae, ordinary stars like our own (when they get to their red giant phase), and young, hot, massive stars before they become supernovae (through very strong 'solar winds').

    It seems that supernovae are needed to distribute 'metals' (which is what astronomers call all elements beyond He) into the inter-galactic medium (IGM), though galaxy collisions will also do the trick.

    One of the sets of tests of our understanding of how galaxies and clusters of galaxies work is to look at the composition of the ISM and IGM in various galaxies and clusters, compare this with the observed numbers of stars by type, and see if things match. So far the theories pass the tests fairly well, although galaxies in the early days of the universe haven't been studied much yet.

    The 'expected lifespan of the universe itself' is model-depedent; in some, it's infinite. The recent discovery of 'dark energy' has upset the model applecart somewhat; in some models of 'dark energy', the universe will end in the Big Rip, with even atoms torn explosively apart as the negative pressure of the dark energy exceeds even the binding energy of nucleons! If you're interested in this topic, please read through some of the threads here in GA&C! There's lots of discussion, all for free.
     
  5. Mar 28, 2004 #4
    Thanks, Nereid and Janus, for your replies.

    Both of you are saying that there has definitely been enough time/generations, under the current models, for the heavier elements to have been formed and distributed as measured. You're both clear about that. That's one question answered.

    Still, though, not being trained in physics (I studied maths at uni and only covered the mathematical framework of current models of cosmology ... no real feel), I find it difficult to reconcile the scales of distances and times involved in cosomological theory.

    So, can I ask pose the questions in a different way?

    Given the tons of evidence that confirms Big Bang Theory as the current best model of the universe, are we not living in what must be the very earliest stages of the universe's full history (using the sun's lifespan as a measure)?

    Qualilitively speaking, it does seem remarkable to me that the universe is only 4 times older than our sun.

    Paul.

    P.S. I hope it doesn't sound like I'm one of those loonies we sometimes get on these forums ... tell me if I do ... and I'll shut up!!
     
  6. Mar 28, 2004 #5
    Stellaration...



    My understanding is that the Terran Star (Sol), is a third generation star. This means that the matter comprising Sol and the Terran star system existed previously in two previous stars which existed prior to Sol's genesis. Also, Sol formed out of a nebula with other stars that have since been re-distributed around the galaxy orbital.

    I speculate that the first two generations were probably a supergiant and giant stars which did not survive long before becoming nova.

    The energy released in radioactive decay and nuclear fission processes on Terra are actually energy that has been stored in these nucleii from these supernovae events.

     
  7. Mar 28, 2004 #6

    Nereid

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    These are good questions!

    In my earlier post I said "The 'expected lifespan of the universe itself' is model-depedent". The Astronomy Picture of the Day item on the Big Rip has some good links which examine this in more detail. For example, this link is to a poster summarising the four eras of the universe (we live in the fourth), and this to one fate of the universe - total darkness, but a very long time in the future. A sorta middle of the road view.
     
  8. Mar 29, 2004 #7

    DrChinese

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    One of the great successes of the current standard model of the Big Bang is its ability to reconcile the observed distribution of elements with theory.

    The current estimated age of the universe is 13.7 billion years.

    You are absolutely correct about there being something significant about the age of the universe and the age of our sun. Our sun is one of the "earlier" (being a relative term) stars of its type to have a planet with a distribution of matter conducive to evolving life. This lessens the likelihood that other intelligent life will be discovered in the next thousand years. Presumably, it takes a long-lived star like ours to support the long periods needed for evolution into intelligent species. Lightweight stars like ours are relatively rarer than fast-burning larger ones.
     
  9. Mar 29, 2004 #8

    Nereid

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    To expand a bit on what DrChinese said ... the first stars (called "Population III" by astronomers) are thought to have been nearly all very massive, and because there we no "metals" (elements heavier than He), no terrestrial planets. The 'second' generation of stars ("Population II") formed with a 'stellar mass function' (~= number of stars of mass m, by m) closer to what we see with the current generation of stars ("Population I"). These mass distributions are dominated - in number - by faint red dwarf stars, which may well 'live' for ~< 1 trillion years. There are relatively fewer stars like our Sun, and even fewer still of the bright, massive type which are so visible from great distances. You can get an idea of the mass function from this list of the nearest 100 stars - see how many are type M and K (the faint, red stars), and how few are O and B (or even A). Our Sun is a "G", between A and K.
     
  10. Apr 1, 2004 #9
    Thanks again, everyone, for the replies. The links were bang on as well.

    I've been taking a bit of time to try and grasp the timescales involved ... it's actually really hard, but I'm glad that I wasn't totally off the track. Dr. Chinese's comment about the time it must take for an intelligent life to develop was, I suppose, what was driving my question in the first place.

    I got a scrappy 'picture' of things studying just some of the maths involved in cosmology... we did relativity, stuff about the current epoch and a bit about the possible fates of the universe (open, closed, entropy, etc), but there's a gaping hole in the middle. Amazingly, it's pretty much the first time I've actually read anything about the epochs in between! It's very interesting ... I'll have to have a good read around.

    Paul.
     
  11. Apr 11, 2004 #10

    Nereid

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    Just to add ... a significant goal of recent research in astronomy has been the universal stellar formation rate, over time; i.e. the average number of new stars formed each year since the CMBR. Needless to say there's quite a lot involved in this question - including a more accurate way of asking it!

    Some SDSS-based research gives an improved answer: the maximum rate at which stars were formed was ~5 billion years ago, and the rate was ~7 times greater than it is today.

    It's been all 'downhill' since the Earth was formed :wink:
     
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