Original sentence: Once the gas is hot enough for the internal pressure to support the fragment against further gravitational collapse (hydrostatic equilibrium), the object is known as a protostar
Edited sentence: A core region forms with gas falling toward the center.During the collapse, the density of the cloud increases toward the center and thus the region becomes optically opaque first.It continues to increase in temperature as determined by the virial theorem.The thermal energy dissociates the H2 molecule, then ionizes the hydrogen and helium atoms.These processes absorb the energy of the contraction, allowing it to continue on timescales comparable to free fall velocities.This continues until the gas is hot enough for the internal pressure to support the fragment against further gravitational collapse—a state called hydrostatic equilibrium.When the accretion phase is nearly complete, the object is known as a protostar