Stellar equilibrium is also known by its other term hydrostatic equilibrium. A star is considered to be in equilibrium when the pressures located in the star balance out the force of gravity. The pressure is thermal pressure that results from the mixture reactions that is happening in the star's core.
A star will remain in equilibrium until such time when the supply of hydrogen in the core is exhausted. After that the star will start to collapse and heat up until another fusion reactions begin.
The balance between pressure cause heat and gravity caused by the stars mass
