starformation

Star formation is the process by which dense regions within molecular clouds collapse under gravity to form stars. Giant molecular clouds supply the raw material, while turbulence, magnetic fields, and external pressure influence the collapse. A region becomes gravitationally unstable when its mass exceeds the Jeans criterion, and fragmentation often yields multiple dense cores that form stars or small systems.

During collapse, a protostar forms at the center of each fragment. Material from the surrounding envelope accretes through a disk, and bipolar outflows carry away angular momentum. The evolution is often categorized into classes (0, I, II, III) corresponding to diminishing envelopes and growing visibility; low-mass stars take roughly a few hundred thousand to a million years to reach the main sequence.

Massive stars form in dense, crowded environments and can disrupt their surroundings with intense radiation, winds, and ionization, creating H II regions and influencing nearby gas. This feedback can both suppress and trigger further star formation.

Observations in infrared and radio reveal dust and gas in star-forming regions; theories and simulations describe the initial mass function and empirical star-formation laws such as the Kennicutt–Schmidt relation. Most stars in the universe are believed to form through these processes within molecular clouds.