1. Dust and gas cloud is present in a galaxy
2. Interstellar matter clump together to form clouds called nebulae
3. Gravitational attraction between the gas/dust particles draws them together
4. Cloud becomes more concentrated, as the particles get closer
5. Temperature and pressure of the cloud increases
6. Fusion occurs as the light (mainly hydrogen gas) nuclei fuse together to form helium nuclei
7. Eventually the star runs out of gas to fuse, and collapses if massive (supernova, neutron star or black hole) or swells to a red giant and then contracts to a white dwarf if normal-sized