What structure do mid-sized stars, like the Sun, puff up into after their core hydrogen fuel is spent?

Answer

Red giants

When core hydrogen is depleted in Sun-like stars, the core contracts, fusion moves to a shell, and the outer layers expand significantly into a red giant phase.

What structure do mid-sized stars, like the Sun, puff up into after their core hydrogen fuel is spent?
astronomylifespanstarcelestial body