The Birth of a Star B uried deep within the dark, almost black expanses of interstellar clouds are hundreds to thousands of local regions, called globules , that are contracting under their own gravity. Such contractions are the beginning of the formation of new generations of stars. The two principal forces are gravity and pressure . Gravity is an attractive force that attempts to contract the gas and dust.
Pressure has the opposite effect.
It tries to disperse the matter. When gravity and pressure are roughly in balance, the gas and dust are stable. There is little contraction or expansion. 1995-1999 TRW Inc.