CNO cycle requires the presence of carbon, nitrogen and oxygen to undergo hydrogen fusion. Does this mean that for first generation stars, no matter how big they are, can't undergo hydrogen fusion by CNO cycle because there is no carbon, nitrogen and oxygen present?
I can't seem to find any website which mentions this. All they say is if a star is large enough, it will undergo hydrogen fusion via CNO cycle, they don't specifically mention it having to be a second generation star.
Answer
It does require carbon to have CNO cycle fusion (it doesn't require nitrogen or oxygen, as they come from the carbon). So you are right, the very first stars could not do CNO-cycle fusion. However, it doesn't take much carbon to make it work, because the fusion is so extremely temperature sensitive that a paucity of carbon is easily made up for by a slight increase in temperature. But you do have to have a little bit of carbon from some prior stars, the Big Bang doesn't make essentially any.
No comments:
Post a Comment