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Thread: Stellar Nuclear Fusion

  1. #1 Stellar Nuclear Fusion 
    Forum Masters Degree MrMojo1's Avatar
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    I was reading the article listed below and noticed the comment "oxygen-to-iron ratio" in the details. The question I have is do stars fuse more than one element at a time?

    NASA - Hubble Finds Birth Certificate of Oldest Known Star


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    Life-Size Nanoputian Flick Montana's Avatar
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    Stellar nucleosynthesis is actually pretty complex. I would really recommend reading up on it. It's extremely fascinating.


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    Forum Masters Degree MrMojo1's Avatar
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    Quote Originally Posted by Flick Montana View Post
    Stellar nucleosynthesis is actually pretty complex. I would really recommend reading up on it. It's extremely fascinating.
    I was wondering how much Iron fusion would be the tipping point before a collapse of all the other layers of elements.
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    Life-Size Nanoputian Flick Montana's Avatar
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    I was under the impression that iron was the last element formed during the collapse itself.
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  6. #5  
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    Quote Originally Posted by MrMojo1 View Post
    Quote Originally Posted by Flick Montana View Post
    Stellar nucleosynthesis is actually pretty complex. I would really recommend reading up on it. It's extremely fascinating.
    I was wondering how much Iron fusion would be the tipping point before a collapse of all the other layers of elements.
    As Flick Montana noted, iron has the most stable of all nuclei, so it is the end of the line, so to speak. Fusion (and fission) of iron requires net energy. Once a star has fused everything lighter and starts to (try) to fuse iron, the core temperature must drop, and fusion stops thereafter. Depending on the initial size of the star, collapse can follow very rapidly after that.
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  7. #6  
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    Clearly iron does get fused sometimes, or there would be no heavier elements out there. But that's a really big star to have that much gravity to make such a thing happen.
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    Quote Originally Posted by tk421 View Post
    Quote Originally Posted by MrMojo1 View Post
    Quote Originally Posted by Flick Montana View Post
    Stellar nucleosynthesis is actually pretty complex. I would really recommend reading up on it. It's extremely fascinating.
    I was wondering how much Iron fusion would be the tipping point before a collapse of all the other layers of elements.
    As Flick Montana noted, iron has the most stable of all nuclei, so it is the end of the line, so to speak. Fusion (and fission) of iron requires net energy. Once a star has fused everything lighter and starts to (try) to fuse iron, the core temperature must drop, and fusion stops thereafter. Depending on the initial size of the star, collapse can follow very rapidly after that.
    That is the understanding that I have, yet the article mentions a oxygen to iron ratio. I take this to me that the light from that star was analyzed and a frequency relating to iron was received, thus iron is present. So at what point, how much mass of iron in a core, in relation to other nucleosynthesis of lighter materials, would sufficient amount of iron could be present before gravitational collapse?
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  9. #8  
    Forum Bachelors Degree Kerling's Avatar
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    Yes whenever a fusion possibility opens, the old ones persist (until the fuel is out).
    The deeper inside the star the more heavy elements fuse together, until iron. It has be hypothesized that the immense pressure inside an old Iron core could actually cool the star due to synthesis of heavier nuclei that better stabalize the pressure inside the star. But still, this indeed is a remarkably old star. Must have had lunch several times.
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    Forum Sophomore laza's Avatar
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    Yes but only very massive stars get to the stage of fusing iron.
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    Quote Originally Posted by PhDemon View Post
    I thought elements heavier than iron were only formed in supernova explosions, but I could be wrong...
    You're correct. Iron is as high as stellar fusion can take elements.
    Its the way nature is!
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    Quote Originally Posted by PhDemon View Post
    I thought elements heavier than iron were only formed in supernova explosions, but I could be wrong...
    Yep. When a star goes supernova, two things happen. First, gravity overwhelms the outward pressure and the star briefly collapses. This collapse is very fast and makes the matter very dense.
    This critical moment is when elements higher than iron are produced.
    Gravity is then overwhelmed by the outward pressure and after the initial implosion, there is the explosion of material outward spreading the newly created heavy elements into space.
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    Quote Originally Posted by PhDemon View Post
    I thought elements heavier than iron were only formed in supernova explosions, but I could be wrong...
    I thought this, too.
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  14. #13  
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    My understanding is that elements heavier than Iron do get formed by other means - by the s-process (slow neutron capture) late in the life of low to medium mass stars.
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