Life Cycle of Stars — AQA GCSE Physics (Separate)
Stars go through a life cycle that depends on their mass. The Sun and much larger stars follow different paths.
Star formation
A star forms from a cloud of dust and gas (a nebula) pulled together by gravity. As it collapses it heats up to form a protostar, and when hot and dense enough, fusion begins and a main sequence star forms.
Main sequence
During the main sequence (the longest, stable phase), the star fuses hydrogen into helium. It is stable because the inward force of gravity is balanced by the outward pressure from fusion.
The path depends on mass
A star about the size of the Sun: main sequence → red giant → (shed outer layers) → white dwarf → (cools) → black dwarf.
A star much larger than the Sun: main sequence → red supergiant → supernova (a huge explosion) → neutron star, or (if massive enough) a black hole.
Importance of supernovae
A supernova scatters the elements made in the star (and heavier ones formed in the explosion) into space. These elements form new stars, planets and everything on them — including us.
Exam tips
- Star formation: nebula → protostar → main sequence (gravity vs fusion balance).
- Sun-sized star: → red giant → white dwarf.
- Massive star: → red supergiant → supernova → neutron star or black hole.
- Supernovae spread heavier elements to form new stars and planets.