Protostjärnefasen

Protostjärnefasen, also known as the protostar phase, is the initial stage in the formation of a star. This phase begins when a dense core within a molecular cloud, known as a Bok globule, collapses under its own gravity. As the core collapses, it heats up due to the conversion of gravitational potential energy into thermal energy. This heating causes the core to become opaque to its own radiation, leading to a rapid increase in temperature and pressure at the center.

During the protostar phase, the core continues to accrete mass from the surrounding molecular cloud. This accretion process is not uniform and can lead to the formation of a circumstellar disk, which may eventually give rise to planets. The protostar phase typically lasts for about 100,000 to 1,000,000 years, depending on the mass of the forming star.

As the protostar continues to accrete mass, it eventually reaches a point where the internal pressure and temperature are sufficient to ignite nuclear fusion in its core. This marks the transition to the main sequence phase, where the star becomes a fully-fledged star. The duration of the protostar phase is relatively short compared to the main sequence lifetime of a star, but it plays a crucial role in the early evolution of stars and the formation of planetary systems.