How does a natural ""solar thermostat"" keeps the core fusion rate steady in the sun?

Explanation:

What is solar thermostat?

A solar thermostat automatically regulates temperature of the sun when the temperature reaches a certain point and its also known as gravitational equilibrium.

NOTE: if the core temperature decreases, then the fusion rate decreases and this lowers the pressure and the cause the core to contract and heat up.

Also, the increase in core temperature, increases the fusion rate and this raise the core pressure and this cause the core expands and cools down.

The fusion rate of the sun increase when core is a bit hotter. This increase in the rate of fusion produces more energy, which cause the core to expand slightly and cool.

The fusion rate is then slow down due to the cooling until the sun get back to it's original size and temperature. The fusion that occur in the sun concerts hydrogen into helium, energy and neutrinos.