What are the stages in the life cycle of a star?

The stages in the life cycle of a star are stellar nebula, average star, red giant, and white dwarf or supernova.

The life cycle of a star begins in a stellar nebula, which is a cloud of dust and gas in space. This nebula is the birthplace of stars. The gravity within the nebula pulls the dust and gas together to form a protostar. As the protostar continues to gather more material, its temperature and pressure increase, leading to the next stage.

The protostar then becomes an average star, or a main sequence star, like our Sun. This stage is characterised by the process of nuclear fusion, where hydrogen atoms combine to form helium, releasing a tremendous amount of energy in the form of light and heat. This stage can last for billions of years, depending on the size of the star.

As the star exhausts its hydrogen fuel, it expands and cools to form a red giant. The star's core contracts while its outer layers expand and cool, giving it a reddish appearance. For smaller stars, this stage ends when the helium fuel is also exhausted, and the star sheds its outer layers, leaving behind a hot core.

This hot core is known as a white dwarf. It is the final stage for smaller stars. The white dwarf cools and dims over billions of years, eventually becoming a black dwarf.

For larger stars, the red giant stage can lead to a supernova. This is a powerful explosion that occurs when a star has used up all its fuel and collapses under its own gravity. The supernova can outshine an entire galaxy and create elements heavier than iron. The remnants of a supernova can form a neutron star or, in the case of the most massive stars, a black hole.