How does hydrostatic equilibrium regulate the sun's temperature if it has a "fever"?...?

Question

How does hydrostatic equilibrium regulate the sun's temperature if it has a "fever" (that is produces too much fusion energy)?

Answer 1

More fusion energy would make the Sun hotter. When a confined gas heats up in a constant volume, it increases the pressure. But since the Sun is free to expand, it does that instead of increasing the pressure in the core. The expansion cools the Sun the same way that expanding freon in a refrigerator cools. This reduces the reaction rate, which reduces the pressure. But since the Sun is free to shrink under its own gravity, it does that instead of cooling. The result is a balance between the heat of fusion reactions trying to puff it up and gravity trying to squeeze it down.