Why does a red giant become big?

1 Answer

The star is in equilibrium durimg mian sequnce


Pressure from fusion push outwards. Gravity pulls inwards..So the star is in equilibrium When most of the hydrogen is finished the the mass become less.THis reduce gravity.The pull inwards is reduced.Pressure from fusions stii continuing'. and the star expandsenter image source here and become a red giant,.
picture credit slideplayer.com.