Basics of Star Formation Text of HST press release. The star formation process is amazing. The formation is driven by gravity . When gravity wins, the clouds contract. ISM clouds are in hydrostatic equilibrium and require some sort of trigger to start the process.
Triggers compress the clouds which increases the inward pull of gravity.
The outer part of the cloud continues to rain down on the central object. It is conceivable that the Upper Mass Limit for Main Sequence Stars is due to the fact that the time required for the central portion of the cloud is so short that the object turns on and becomes a star before the outer layers of the cloud can fully merge with the star. The lower mass limit arises because stellar material cannot be compressed beyond certain limits. It is very difficult to compress electrons beyond densities of several hundred thousand times the density of water. This resistance to compression is independent of the temperature of the gas as it is due to the level of packing of the particles.