GCSE Physics · Edexcel 1PH0 · Topic 7B
The life cycle of stars
Key points
- Stars form in a nebula, a cloud of dust and gas pulled together by gravity, forming a protostar.
- When it is hot enough, hydrogen fuses into helium and it becomes a main sequence star. It is stable because outward pressure from fusion balances inward gravity.
- Stars like the Sun: main sequence → red giant → white dwarf (cools to a black dwarf).
- Much more massive stars: main sequence → red supergiant → supernova → neutron star or black hole.
- Supernovae spread heavier elements into space, which form new stars and planets.
- The Hertzsprung–Russell idea links star colour (temperature) and brightness; bluer stars are hotter.
Topic notesPremium
Stars are born, shine for millions or billions of years and then die. What happens to a star depends almost entirely on its mass, and throughout its life there is a contest between gravity pulling in and pressure pushing out.
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