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What happens to a star when all the hydrogen has been converted to helium?

Answer 1

Giants.

The star reorganizes itself when all of the hydrogen is converted to helium; its core contracts and its outer layers expand, causing the star to become either a giant or a super-giant, depending on its initial mass. In this state, the star will begin to burn helium to carbon and, if sufficiently dense, from carbon to other heavier elements; a star the size of our Sun will burn helium to carbon but not carbon to other elements.

Larger stars will be dense enough to burn carbon and reach a point where their cores are only made of iron. At that point, they will explode because the inward acting gravity will not be balanced by fusion reactions.

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Answer 2

Leah Abbate

After expanding into a red giant, the star's outer layers are shed, creating a planetary nebula, and the remaining core of the star turns into a white dwarf.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.