Every night we look into the sky full of twinkling Stars, dazzling our mind. The wonderful sparkling night sky is due to the formation of discrete set of stars from the intersteller molecular clouds or dusts.The fight between the inward gravitational force and the outward pressure force decides the fate of a star. Gravity brings the particles in the molecular clouds closer while the pressure waves radiated from the random agregation of the particles, tend to oppose the gravity. The balance between the two forces creates a protostar which is said to be in Hydrostatic Equilibrium.

Protostar is fully opaque and hence trasfer of energy via radiation is impossible. Thus energy is trasfered outward via convection and the protostar is said to be in convective equilibrium.

The convective equilibrium time period is fully dependent on the mass of the protostellar object. More the mass, less will be the time spent in convective equilibrium. Gravitaion still continue to contract the protostar. During this contraction a radiative core starts to develop. And as the radiative core grows enough to push the convective layer outward or throw it out of the protostar the protostar is said complete its pre- main sequence evolution. After this stage the star still continue to contract and increase its internal temperature. When the internal temperature becomes high enough to ignite the Hydrogen a thermo nuclear reaction or burning of hydrogen begins. At this stage radiation carries the energy outward and thus balancing the inward pull of the gravity. For the first time the star is said to attain an equilibrium between the two forces. The protostar settles in the Main sequence of the HR diagram and becomes a STAR. This way Stars are formed.