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Thread: Composition of Stars

  1. #1 Composition of Stars 
    Forum Masters Degree MrMojo1's Avatar
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    If a Spectrometer is used to get an idea of what element a star is fusing, then are there stars no longer fusing hydrogen? I know we have identified different types of neutron stars, but has anyone explained that they are composed of iron?


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    Comet Dust Collector Moderator
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    Neutron Stars are composed of....wait for it....neutrons.


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    Forum Masters Degree MrMojo1's Avatar
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    Quote Originally Posted by MeteorWayne View Post
    Neutron Stars are composed of....wait for it....neutrons.
    Thanks for the thoughtful explanation.
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    Moderator Moderator Dishmaster's Avatar
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    Quote Originally Posted by MrMojo1 View Post
    If a Spectrometer is used to get an idea of what element a star is fusing, then are there stars no longer fusing hydrogen? I know we have identified different types of neutron stars, but has anyone explained that they are composed of iron?
    One can imagine such stars, but actually, stars begin to fuse other elements a long time before all hydrogen is depleted. This is because the fusion can only work in a certain sphere around the nucleus inside the star. Stars like ours will at some point deplete its hydrogen reservoir in its core and start to fuse helium. Since a higher temperature is needed for this, the pressure in the core of such a star must rise before this can happen. This can only be accomplished by compressing the stellar matter by gravity. This compression increases the density and temperature in the shell around the helium burning core so that hydrogen can fuse within this shell. This produces a stronger radiation pressure towards the outer layers of that star causing it to bloat to a red giant star. This can go on depending on the total mass of the star, but only up to iron (our sun stops already at carbon or oxygen). So the ultimate fate of a stellar core can be iron. As soon as this stage is reached the radiative pressure from inside that balances the gravitational pressure from upper layers stops and the star collapses. This is a supernova of type II. During the collapse, the core is compressed so much that protons and electrons combine to neutrons. A neutron star remains.
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    Forum Masters Degree MrMojo1's Avatar
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    Thanks. I wasn't aware that other elements were being fused at the same time as hydrogen. Would this account for the periods of time of high/low solar output of our sun?
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    No, that's based on intenal flow of material in the "mantle" will above the area where fusion occurs. Fusion happens basically at the center where the pressure and temperature is high enough, Above that is a whole mess of convection
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