What mechanism allows a protostar to achieve a temporary, intermediate equilibrium before fusion begins?

Answer

Pressure of gravitationally heated gas

Since the core of a protostar is not yet hot enough for fusion, it reaches a temporary balance against gravity using the outward thermal pressure created by the gas that has been heated through continued gravitational compression.

What mechanism allows a protostar to achieve a temporary, intermediate equilibrium before fusion begins?
protostarstellar evolutionstar formationastrophysicscollapse