Age of the sun+age of previous stars = universe ?

  • Thread starter curiousOne
  • Start date
20
1
I'm always perplexed by the numbers I see on estimates of the age of the universe and the age of our solar system.
Somehow, I don't see it adding up. Here's my logic, plese point out the flaw:

1- Current estimate of the age of the universe : 13.73 billion years give or take.
(when I was in high school, it used to be 15.4).
2- Current estimate of the age of the sun: 4.57 billion years.
3- Current estimate of the life expectancy of an average star like the sun: 11 billion years. Let's just say 10 billion years.

Now to explain the heavy materials found on earth, that aren't formed in the sun, i.e. those that came before the sun was formed, the usual assumption is to say that another star/stars previously left that stuff behind before going supernova. Add a little more stuff from the galactic dust and here you go, you have titanium on earth.
The problem is that for other stars to have been able to leave that stuff behind, they would have had to go through their complete life cycle, and then the material would have accumulated long enough to form our system.
So, subtract 4.57 from 13.73, and that leaves 9.6 or so billion years for a star to form, expel titanium out and for the remaining cloud to accrete into becoming our solar system.
You could say, that's fine, that's just enough time, but for heavy elements, I thought these could not form on a first generation star, because there are no intermediate elements to fuse from.
So it doesn't add up.

Can someone clarify ?
 

turbo

Gold Member
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It's a good question. There are currently distant galaxies, quasars, etc at redshift z>6 (less than a billion years after the BB by current reckoning) that according to their spectra have super-solar metallicities. Since lots of high$$$$ observing programs are geared toward teasing out high-redshift objects so that they can be re-examined, if necessary, these observations are pretty intriguing. It's not just one or two outliers, but whole classes of high-redshift objects that exhibit this trend. So far, quasars have shown no redshift-dependent evolution in either absolute or relative metallicities (according the the principals of the SDSS consortium), so there are some pretty big cosmological questions posed by such observations. These include: Do we understand stellar evolution? Do we understand the role of supernovae in metal-enrichment of later generations of stars? Is the heirarchical-formation hypothesis (large objects grow from smaller objects) viable?

You may be interested in this paper:
http://arxiv.org/abs/0901.0974
 
Last edited:

D H

Staff Emeritus
Science Advisor
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All stars are not created equal. Big stars age burn faster and die faster, a whole lot faster, than do small stars such as our Sun. In "The First Generations of Stars", Science 15 July 2005, Timothy C. Beers writes "The first stars in our universe that formed shortly after the Big Bang were probably very massive and short-lived." (http://www.sciencemag.org/cgi/content/summary/309/5733/390).

That we have gold, uranium, and other elements heavier than iron on our planet and in our solar system is indicative that our Sun's predecessor, a second generation star, was also a large (and hence short-lived) star. Those massive elements are only produced in supernovae. A small, long-lived star such as our Sun cannot end its life with a supernova.
 
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life expectancy of an average star like the sun: 11 billion years.
I would have guessed that the brightest light burns the shortest. Does http://www.astronomynotes.com/evolutn/s2.htm" [Broken] solve your problem?
 
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Borek

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IIRC (but I can be wrong) the higher the initial mass the shorter the life span of the star. Add to that fact, that stars with mass more then 10 solar masses (or something around) will end as supernovae - and your problem disappears.
 
Just to sum up what everyone else has said already and to augment it slightly:

1. The dust and heavier elements that helped form our planets came from other stars.
2. Other stars/early stars were massive (8 solar masses and higher).
3. Massive stars burn bright and quickly, and so they have a short "lifespan" that is much less than the age of the universe.
4. Massive stars are capable of contracting from a Hydrogen/Helium core to Carbon/Nitrogen/Oxygen and finally to Iron.
5. Any star capable of forming an iron core ends up as 3 possible things: a neutron star, a black hole, or a supernova.
6. If the star contracts and rebounds as a supernova, all the elements beyond Iron are formed.
7. The final momentum of the supernova explosion gives inertia to these elements and particles, causing them to be distributed amongst interstellar material and goes on to forming other stars and eventually planets.

I hope all our contributions helped answer your question :)
 
20
1
Great, thanks for all who replied. It certainly sounds like the best explanation.
However, questions remain:

1- Is this confirmed by observation ? For instance is the spectra of distant galaxies indicative of the lighter elements bias ?
2- How about the time it takes for expelled supernovae matter to accrete ? It seems with the distances involved (even taking account of expansion) it would take a very long time for systems to form. It would seem that the time spent to accrete such masses would be much longer than the star's life, even if they overlap.
3- Huge , short lived stars would have to leave enormous black holes behind. Are we saying that the core of modern galaxies are probably the one and same thing as these 1st or second gen stars ? Again, due to expansion, the density of galaxies should be much higher with the distance then. Is that confirmed by observation ?
 

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