What happens to a star if its core fusion rate slightly increases above equilibrium?

Answer

The outer layers expand, cooling the core and reducing the fusion rate.

An increase in fusion pressure causes the star to expand slightly. This expansion cools the core plasma, which in turn reduces the fusion rate until the pressure balances the gravitational force once more.

What happens to a star if its core fusion rate slightly increases above equilibrium?
hydrogenCoresequencestarFusion