A protostar is an early stage in the formation of a star. It forms from a dense region within a molecular cloud, where gravity pulls together gas and dust. As the material accumulates, it heats up, creating a hot core. This process can take millions of years, and during this time, the protostar is surrounded by a rotating disk of material. As the protostar continues to gather mass, it eventually reaches a temperature and pressure high enough for nuclear fusion to begin. This marks the transition from a protostar to a main sequence star, like our Sun. The surrounding disk can also give rise to planets, moons, and other celestial bodies within the solar system.