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Protostars typically form from molecular clouds consisting primarily of molecular hydrogen. When a molecular cloud reaches a critical size, mass, or density, it begins to collapse under its own gravity. As the cloud shrinks, conservation of angular momentum causes the random motions originally present in the cloud to become one coherent rotation. This rotation causes the cloud to flatten out (much like forming a flat pizza out of doughDough is a paste made out of any cereals (grains) or leguminous crops by grinding with small amount of water. This step was a precursor to making of breads, pastries and cookies. In many parts of central India, native people, use the quick method of makin) and take the form of a disk.

Further gravitational interactions may cause the dust and gas in the disk to condense into planetesimalIn cosmogony, planetesimals are objects thought to exist within solar nebulae. Planetesimals are thought to form from the coalescing (due to collisional sticking and gravity) of particles, orbiting within the accretion disc of the solar nebula; an accumuls. This process competes against the stellar wind, which drives the gas out of the system, and accretionIn astrophysics, accretion is the gravitational process by which bodies such as planets and stars form from gas and dust. See also accretion disc In atmospheric science, accretion is the growth of a precipitation particle by the collision of an ice crysta, which pulls material into the central protostar.

See also:

• accretion discAn accretion disk (or accretion disc is a structure formed by material falling into a gravitational source. Conservation of angular momentum requires that, as a large cloud of material collapses inward, any small rotation it may have will increase. Centri
• planetesimalIn cosmogony, planetesimals are objects thought to exist within solar nebulae. Planetesimals are thought to form from the coalescing (due to collisional sticking and gravity) of particles, orbiting within the accretion disc of the solar nebula; an accumul
• protoplanetIn cosmogony, a protoplanet is a quasi- planetoid which is slightly larger than a planetesimal and orbits within a solar nebula's protoplanetary discs. Such objects are formed by the accretion of objects (such as dust and planetesimals) within the accreti
• solar nebula