What causes the core of a star to contract and heat up after hydrogen fusion ceases there?

Answer

Gravity begins to win the battle against thermal pressure

When the hydrogen fuel in the core is depleted, the internal thermal pressure drops, allowing gravity to cause the core to contract and increase its temperature immensely.

What causes the core of a star to contract and heat up after hydrogen fusion ceases there?
astronomystarsFusionred giantshelium