What is the first stage in the life cycle of a star?

The first stage in the life cycle of a star is a cloud of dust and gas, often referred to as a nebula. This stage is critical because these clouds contain the necessary materials, primarily hydrogen and helium, which are the building blocks of stars. Over time, under the influence of gravity, regions within the nebula begin to collapse and heat up, leading to the formation of a protostar.

The process starts when gravitational forces cause the particles within the cloud to draw closer together, increasing pressure and temperature at the core. It’s this accumulation and subsequent increase in density and temperature that initiates the birth of a new star. The other concepts, such as neutron stars, black holes, and main-sequence stars, occur at much later stages in stellar evolution, meaning they do not represent the initial phase of a star's life cycle.