what will happen to the sun when the fusion of hydrogen into helium slows down?

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  • 1 decade ago
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    The fusion of hydrogen produces a counter pressure to gravity, so that the Sun is a stable star.

    When most of the hydrogen fuel in the core has been used, fusion stops. As the counterforce has disappeared the inert helium ash that has built up in the core will start to collapse under its own weight. This causes the core to heat up and to ignite the hydrogen in a thin shell around the core. The Sun grows slowly and becomes first a Yellow Subgiant and then a Red Giant.

    In the giant stage our Sun will expand to the size of the orbit of the Earth.

    Inside the collapsing core the temperature is now high enough so that helium can fuse. When the Sun runs out of this type of fuel, after another billion years, it is near the end of its life.

    The Sun begins to throw off layers because it can't support them anymore. This is called a planetary nebula. The core of the star becomes a white dwarf. This is an extremely dense star the size of a planet. Finally, when the white dwarf has used all its energy, it stops shining and becomes a "black dwarf", a dead star. This is expected to be the final state of our Sun.

    In another 30 billion years or so.

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  • Lutty
    Lv 4
    4 years ago

    HK - Of your choices, there is only one viable nuclear fusion reaction listed... Hydrogen turns into Helium... I would have said is fused into Helium, but I guess this is close enough. Helium turns into hyrdogen is backward. Fusion will never turn Helium into Hydrogen. Helium is fused into Carbon under a process called the Triple Alpha process... and the other answer is correct - the sun is too small for this to ever happen... Oxygen into carbon dioxide is half of a chemical (not nuclear) reaction... O2 + C + heat --> CO2(g) The last one is just wrong!! Hope this helps...

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  • 1 decade ago

    The core will contract and heat up, igniting the fusion of hydrogen in the shell around the core. This will cause the Sun to expand into a red giant.

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  • 1 decade ago

    Two forces that kep Sun a present size is the pressure from fusion outwards and the pull of gravity inwards.When fusion slows down, the pressure reduces and Sun becomes white dwarf.

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  • 1 decade ago

    When the sun runs out of lighter elements to fuse, it will instead start fusing larger elements, causing the sun to expand with the increase in energy, and will form a red giant. For your information, this expansion would encompass the orbits of mercury, and probably earth.

    eventually, when all that fuel runs out, it will collapse, as it does so getting hotter, forming a white dwarf.

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