How is stellar equilibrium finally reached?
When gravity makes the core of a star so hot and dense that nuclear fusion commences, that pressure balances gravity and establishes equilibrium.
This is how stars are born. As the interstellar gas (which is mostly hydrogen-1) collapses under its own gravity, the potential energy released is converted to heat and the gas becomes denser. With enough mass (about 80 times the mass of Jupiter), the gas reaches millions of degrees and a high density, conditions that enable the hydrogen-1 to fuse to helium. The energy released by that fusion creates the pressure necessary to balance gravity.