What is the first stage in the life cycle of a star, starting from a stellar nursery?

The first stage in the life cycle of a star that begins in a stellar nursery is the protostar phase. Stellar nurseries, or molecular clouds, are regions of space dense enough to allow gravity to cause the gas and dust to condense. As this material accumulates, it forms clumps that collapse under their own gravity, leading to an increase in temperature and pressure.

During the protostar phase, the core of the forming star heats up, but nuclear fusion has not yet begun. The protostar continues to gather material from the surrounding environment, and as it grows, it contracts and heats further. This stage lasts for a relatively short time in astronomical terms, but it is crucial as it sets the foundation for the subsequent evolution into a main-sequence star, where hydrogen fusion begins to occur in earnest.

Understanding this phase is essential because it represents the transition from a cold, dense cloud of material to a hot, forming star, influencing the characteristics of the future star and potentially its eventual stage of evolution. The other stages mentioned, such as red giant, main-sequence star, and supernova, occur later in a star's life cycle, following the protostar stage.