Page "Star formation" Paragraph 17

When the core temperature reaches about, the thermal energy dissociates the H < sub > 2 </ sub > molecules.

This is followed by the ionization of the hydrogen and helium atoms.

These processes absorb the energy of the contraction, allowing it to continue on timescales comparable to the period of collapse at free fall velocities.

After the density of infalling material has dropped below about 10 < sup >− 8 </ sup > g cm < sup >− 3 </ sup >, the material becomes sufficiently transparent to allow radiated energy to escape.

The combination of convection within the protostar and radiation from the exterior allow the star to contract in radius.

This continues until the gas is hot enough for the internal pressure to support the protostar against further gravitational collapse — a state called hydrostatic equilibrium.

When this accretion phase is nearly complete, the resulting object is known as a protostar.