Can stars form from helium instead of hydrogen?

Stars are able to go through their helium byproduct supply after their hydrogen fusion starts to run out of fuel supply, but is it possible for a star to form "from scratch" using only helium? Many have proposed that once the universe "runs out" of hydrogen, there will be no more new stars formed. But what about the other elements left hanging around from previous super nova and other left over sources?

Update:

Hey all, thank you very much for the great answers, that helps a lot!! I brought up the point about the hydrogen running out because I've seen that argued in a number of documentaries. I thought it a bit weird, but put it into the question to help clarify my reason for posting this.

As to the concentration of the other elements being preventive to star formation using other elements, that makes sense, but wold it really be that much less concentrated than the hydrogen "hanging around" prior to the star's formation? Since the mass of the hydrogen has been converted into helium and energy, and the energy has been radiated out as heat, that left over matter would be comparatively as concentrated as the hydrogen before, no?

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  • 7 years ago
    Favorite Answer

    The universe will not "run out" of hydrogen.

    Helium, in large enough quantities to form a star, does not exist without being mixed with hydrogen... a lot more hydrogen than helium.

    Our own Sun will not run out of hydrogen. As the hydrogen fuses to produce energy, it produces helium as a by product. As the amount of helium "ash" accumulates in the core, where it is useless, for now, the helium gets in the way of the fusion process and requires the Sun to ever so slightly increases the pressure and temperature in the core to maintain the fusion process.

    In another 5 billion years, or so, there will be too much helium ash to the hydrogen process to continue normally in the core. Hydrogen fusion in the core will then stop (our Sun will then stop being a "main sequence star". However, at that time, it will still have 90% of its initial hydrogen left!

    By then, most of the helium ash, being denser than hydrogen, will have concentrated in the centre of the core. As the Sun collapses (slowly, when compared to stars that go supernova), the temperature and pressure will eventually be sufficient to trigger helium fusion (producing carbon and a bit of oxygen -- but even then, only part of the helium gets involved). This sudden production of energy will trigger fusion of hydrogen in the upper layers and this will slowly "eject" the outer layers of the Sun back into the interstellar medium. That stuff that goes back out into the universe (making the Sun look like a planetary nebula, when it happens) will still be mostly hydrogen, with a good proportion of helium, but still mostly hydrogen (by number of atoms). Most of the helium and the pinch of carbon stays in the remaining dwarf star.

    There is no process that would cause a separation of hydrogen and helium. Therefore, no "helium stars" forming from scratch.

    Very small stars (smaller than our Sun) have convection currents that reach right into the core. These stars will continue fusing hydrogen (much more slowly than our Sun, being smaller) until well over 90% of the original hydrogen has been changed into helium. However, such star are expected to have lifetimes of hundreds of billions of years (therefore, the universe is still not old enough for these "mostly helium" stars to exist, yet).

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  • 7 years ago

    it can happen. It is just very rare of an occurrence if any as helium is far more a rare element than hydrogen in the universe and the likeliness of enough to converge to form a star is unlikely. Stars that do so however would likely be very bright, large and or very hot.

    The other elements up to fusion into iron would also be possible but even less likely for fusion of such to happen as each element up to iron would be less likely to converge in sufficient quantities.

    novas and supernovas have a nasty habit of dispersing the star's and surrounding matter so formation of a star from just the remnants of a dead star would be near impossible.

    In short, a star can form from scratch fusing helium and heavier elements into even heavier elements but the heavier the element, the less likely it is to happen.

    Source(s): astronomy class
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  • 7 years ago

    It *is* possible, but the amount of free helium in the concentrations needed is likely never to happen.

    The star would need to have immense mass to start helium fusing into carbon, and the mixture of other elements from a nebula would likely make this impossible - the heavier elements would migrate to the center, spreading the helium further out - and away from the needed temperature and pressures - to begin fusing.

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  • 7 years ago

    There isn't that much Helium at one place, exclusive of Hydrogen.

    Helium is formed by fusion of Hydrogen. It is very highly unlikely that all Hydrogen gets converted to Helium, till the last atom of Hydrogen.

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  • hamman
    Lv 4
    3 years ago

    Deuterium and tritium are fusable into Helium. they are the two styles of hydrogen, yet have extra desirable neutrons. seem them up in wikipedia for extra info. additionally seem up Nuclear Fusion in wiki. Sorry the links are not engaged on the 2d, otherwise i could grant them in case you don't understand approximately wiki, then do a yahoo or google seek for wikipedia then take it from there.

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