What eventually halts the gravitational collapse of an interstellar gas cloud that forms an object that is not massive enough to become a star?

The central object becoming hot enough to sustain nuclear fusion in its core

and/or crowding of electrons in the core

Explanation:

Irregularities in the density of the gas causes a net gravitational force that pulls the gas molecules closer together. Some astronomers think that a gravitational or magnetic disturbance causes the nebula to collapse. As the gases collect, they lose potential energy, which results in an increase in temperature.