Why are no stars smaller than about 1/10 the mass of the sun?
Stars are formed by the gravitational collapse matter (dust and gas) in a region of interstellar space. As it collapses it begins to release heat due to the building pressure with the packed matter. The energy from this heat is released for a while as the matter continues to collapse until the center has enough heat and density to begin fusion. Most protostars will then balance the energy from the fusion with the gravitational collapse and reach an equilibrium – the birth of a star. Theoretically, it was calculated that if the total mass is < 0.08 of our solar mass, then the star cannot ignite and just radiates it's heat away - this is called a 'brown dwarf'.
