What happenes in red giant?

Answer 1

In a red giant phase, a star exhausts the hydrogen fuel in its core, causing the core to contract under gravity while the outer layers expand and cool, giving the star its characteristic reddish hue. Helium fusion begins in the core, and the star may go through multiple cycles of fusion, creating heavier elements. This phase leads to significant changes in the star's structure and brightness, often resulting in the shedding of outer layers and the formation of a planetary nebula, while the core may ultimately become a white dwarf.