What is the first stage of a star's life cycle?

The first stage of a star's life cycle is the formation of a protostar from dust and gas. In the vast reaches of space, regions of gas and dust, commonly referred to as nebulae, can begin to collapse under their own gravity. This collapse causes the material to clump together and start to form a dense region. As the density increases due to this gravitational pull, the temperature within this forming body also rises.

This hot, dense region is what we call a protostar, which eventually will continue to gather material and increase in temperature until it reaches the conditions necessary for nuclear fusion to begin. This marks the transition from a protostar to a main-sequence star. Thus, the formation of a protostar from dust and gas is correctly identified as the first stage of a star’s life cycle.