What makes an ordinary star become a red giant?

1 Answer

Answer:

star is normally in equilibrium m due to gravity pulling inwards and pressure from fusion pushing outwards.

Explanation:

When the fuel at center(Hydrogen) is almost finished, the the pull of gravity is reduced due to less mass. But still fusion continue and the star expands outwards..So its temperature is reduced and size increases.enter image source here
picture atnf csiro wu.