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Thread: Basic question about stars...

  1. #1 Basic question about stars... 
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    Ok, I haven't studied any astronomy before as it doesn't come into play untill I start studying for my second state examination (my first one is this June) if I keep on physics. However I am really interested in it, and this morning I was looking at the sun rising and the last few stars and I was wondering since the stars are burning balls of gas, how do they burn if there is no oxygen in space?


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    Genius Duck Moderator Dywyddyr's Avatar
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    Quote Originally Posted by biochem:) View Post
    since the stars are burning balls of gas, how do they burn if there is no oxygen in space?
    I do hope you're being facetious.
    From Wiki: a star shines due to thermonuclear fusion of hydrogen into helium in its core etc etc.


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    Bullshit Intolerant PhDemon's Avatar
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    Stars form when there is enough matter so that under its own gravity it collapses into a ball of gas that is dense enough for nuclear fusion to occur. This is what "powers" stars, it is not burning so no oxygen is required.

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    Universal Mind John Galt's Avatar
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    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by biochem:) View Post
    since the stars are burning balls of gas, how do they burn if there is no oxygen in space?
    I do hope you're being facetious.
    Am I mistaken in thinking that, lacking knowledge we have today, early scientists believed the stars to be burning?

    You seem to feel biochem asked a foolish question. In my view the only foolish question is the one that is not asked. Criticising people for being ignorant of a piece of information does not encourage them to continue asking questions.
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    I don't think my questions here are too off-topic.

    Ok, so stars are nuclear fusion at work, producing heat and light.

    What about nuclear fission? Could a plutonium or uranium star produce heat and light on a continuous basis (let's say for millions of years)?
    Grief is the price we pay for love. (CM Parkes) Our postillion has been struck by lightning. (Unknown) War is always the choice of the chosen who will not have to fight. (Bono) The years tell much what the days never knew. (RW Emerson) Reality is not always probable, or likely. (JL Borges)
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    Universal Mind John Galt's Avatar
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    Quote Originally Posted by jrmonroe View Post
    What about nuclear fission? Could a plutonium or uranium star produce heat and light on a continuous basis (let's say for millions of years)?
    I think not. Here are ac couple of obstacles I suspect would be there.

    Stars are massive. Only hydrogen and helium are present in sufficient concentrations to form the bulk of a star, so adequate concentrations of radioactive components would not be found.

    Since a critical mass is required to produce the fission reaction I cannot envisage how one would arrive at the concentration necessary within a turbulent medium. Concentration occurs in planetary environments, not stellar.

    If you did have the concentration a runaway, explosive reaction seems likely.
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    Moderator Moderator Janus's Avatar
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    Quote Originally Posted by John Galt View Post
    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by biochem:) View Post
    since the stars are burning balls of gas, how do they burn if there is no oxygen in space?
    I do hope you're being facetious.
    Am I mistaken in thinking that, lacking knowledge we have today, early scientists believed the stars to be burning?
    It was considered at one time, along with the idea that its heat came from gravitational collapse. However, geological dating methods came up with an age for the Earth that was greater than the length of time that either of these methods could have maintained the Sun's energy output.
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    Quote Originally Posted by John Galt View Post
    Quote Originally Posted by jrmonroe View Post
    What about nuclear fission? Could a plutonium or uranium star produce heat and light on a continuous basis (let's say for millions of years)?
    I think not. Here are ac couple of obstacles I suspect would be there.

    Stars are massive. Only hydrogen and helium are present in sufficient concentrations to form the bulk of a star, so adequate concentrations of radioactive components would not be found.

    Since a critical mass is required to produce the fission reaction I cannot envisage how one would arrive at the concentration necessary within a turbulent medium. Concentration occurs in planetary environments, not stellar.

    If you did have the concentration a runaway, explosive reaction seems likely.
    Another factor to consider is that only certain isotopes are fissile. For Uranium it is U235, which only makes up ~0.7% of naturally occurring Uranium. We have to enrich Uranium to make it usable as a nuclear fuel. So not only would you have the problem of concentrating the Uranium, but you would also have to have a mechanism for enriching it.
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    Quote Originally Posted by Janus View Post

    It was considered at one time, along with the idea that its heat came from gravitational collapse. However, geological dating methods came up with an age for the Earth that was greater than the length of time that either of these methods could have maintained the Sun's energy output.
    In the 19th Century it was thought that the Sun was made of coal. Like the gravitational collapse model, it eventually proved incompatible with the deep time scales revealed for the Earth.
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    Quote Originally Posted by biochem:) View Post
    .... and I was wondering since the stars are burning balls of gas, how do they burn if there is no oxygen in space?
    They burn quietly, very very quietly. Try listening to them tomorrow morning and you will understand my answer.
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  12. #11  
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    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by biochem:) View Post
    since the stars are burning balls of gas, how do they burn if there is no oxygen in space?
    I do hope you're being facetious.
    .
    I'm sorry. I did say it was a basic question in the title, and also I did mention that I have not done astronomy in school at all, and none a the books I read in the past mentioned stars I was more reading about the planets in our solar system. So I think it was my grandad who told me stars were burning balls of gas and I was working of that, so sorry.

    Also thanks to everyone for answering my question, at least now a won't make the mistake of of thinking they were burning again, saving the embarasment. Thanks again
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    Quote Originally Posted by jrmonroe View Post
    I don't think my questions here are too off-topic.

    Ok, so stars are nuclear fusion at work, producing heat and light.

    What about nuclear fission? Could a plutonium or uranium star produce heat and light on a continuous basis (let's say for millions of years)?
    Given the density of plutonium or uranium, anything approaching the size of our sun would probably collapse into a neutron star if not a black hole. Just maybe a small white dwarf star could fit that description, but somehow I feel that packing radioactive elements that tightly would not be wise.
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    Quote Originally Posted by biochem:) View Post
    Ok, I haven't studied any astronomy before as it doesn't come into play untill I start studying for my second state examination (my first one is this June) if I keep on physics. However I am really interested in it, and this morning I was looking at the sun rising and the last few stars and I was wondering since the stars are burning balls of gas, how do they burn if there is no oxygen in space?
    ~ The question has been answered and fine.. Not Burning as you might have imagined but a gravity driven fusion.. Hydrogen to helium and a quick study and a look in to Wikipedia would answer most related questions as to types of stars.
    I do want to dampen the enthusiasm of answering what was not asked.. It seems to me that only confusion and complexity are the result. If you have questions of types of stars and of what they might be converting in the core of which.. Open a new thread and go for it... ' Biochem ' had the wrong idea and you have put it right... enough.. or you 'over answer'.. and confusion and fusion rain supreme...
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    Quote Originally Posted by jrmonroe View Post
    I don't think my questions here are too off-topic.

    Ok, so stars are nuclear fusion at work, producing heat and light.

    What about nuclear fission? Could a plutonium or uranium star produce heat and light on a continuous basis (let's say for millions of years)?
    There are starlike objects powered by nuclear fission. They are called supernova fragments. The massive pressures of a supernova explosion drive the creation of atomic nuclei much heavier than the iron breakeven point. After the initial flash of the supernova, the fragments radiate energy for quite a long time, largely due to the fission of these newly created nuclei. During the first few years after the primary flash, this radiation appears to be dominated by the decay of cobalt 60.

    As for normal stars, fission probably does occur in them, at least in population I stars, which form in regions seeded with heavy elements by previous supernova events. But the amount of heavy elements present that can release energy via fission is vanishingly small compared to the amount of hydrogen present, so the vast majority of the energy released comes from fusion, and it is hard to see any evidence of fission occurring.
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    It is a bad habit of astrophysicists still talking about "hydrogen burning". However, they know what they mean with this. It might be confusing for people outside that community.
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    Quote Originally Posted by Dishmaster View Post
    It is a bad habit of astrophysicists still talking about "hydrogen burning". However, they know what they mean with this. It might be confusing for people outside that community.
    I've been wondering if you were still here. I hope everything is alright with you.
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    Forum Bachelors Degree GoldenRatio's Avatar
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    Quote Originally Posted by jrmonroe View Post
    I don't think my questions here are too off-topic. Ok, so stars are nuclear fusion at work, producing heat and light. What about nuclear fission? Could a plutonium or uranium star produce heat and light on a continuous basis (let's say for millions of years)?
    If we took our "magical hypothetical star made of refined uranium" I see 2 major problems. Stars work on fusion, not fission. You cannot fuse elements heavier than iron in stars without causing supernove events. The other, being gravity. I see your star blowing up, or collapsing in on itself. Nuclear fission on earth is really just an elaborate steam engine. Thats pretty much it. We replace the wood or coal with fission.
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    I did not see this at first, but fission in stars being 2H → He, and as stars are gas balls, the helium is heavier than the hydrogen and would fall back into the star, and thus, help maintain the integrity of the star. Fission would produce smaller, more energetic particles that would tend to leave a star (as hydrogen and helium escape from our relatively heavier atmosphere). This would cause such a star to lose relatively large amounts of mass relatively quickly. Does this make sense?
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