Life history of a star
1. Gravitational forces pull clouds of dust and gas together to form a protostar.
2. Becomes denser and the nuclei of hydrogen atoms and other light elements start to fuse together. Energy is released so the core gets hotter and brighter.
3.Hydrogen fusion in core> radiate energy. Can last for billions of year until the star runs out of hydrogen nuclei. Star is stable because inward force of gravity is balanced by outward force off radiation from core= main sequence star.
4.Eventually runs out of hydrogen nuclei,swells, cools down and turns red.
5. Red giant .Helium and other light elements fuse to form heavier elements. Fusion stops and star will contract to form a white dwarf
6.Eventually no more light emitted and star becomes a black dwarf.
5. Swells to become a red supergiant which continues to collapse.
6. Eventually explodes into a supernova.Outer layers thrown out into space. Core left as neutron star..If massive enough becomes a black hole.