IGCSE Physics / Stellar evolution
The life cycle of a star like the Sun
Edexcel International GCSE Physics (4PH1), chapter 27: Stellar evolution, specification point 8.9. Free lesson.
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A star with a similar mass to the Sun passes through five stages, from a nebula to a white dwarf. During the main sequence, inward gravity balances outward pressure from fusion, keeping the star stable for billions of years.
The five stages in order
A Sun-like star changes as its fuel and structure change. Learn the stages in order, then link each one to what happens to the star. Nebula: a huge cloud of gas and dust, pulled together by gravity. Protostar: the cloud collapses into a hot, dense ball. It heats up as it shrinks. Main sequence star: the core becomes hot enough for hydrogen to fuse into helium. Red giant: when hydrogen in the core runs out, the star expands and cools. White dwarf: the outer layers drift away, leaving a hot, dense core that slowly cools.
Why a main sequence star is stable
A main sequence star stays about the same size because two effects balance. Gravity pulls the star's material inwards, while energy from fusion heats the gas and creates outward pressure. The star does not collapse or expand while the effects balance. The inward force is gravity, pulling material towards the centre. The outward effect is pressure from hot gas, heated by energy released through fusion in the core. The balance keeps the star stable for billions of years, as long as there is hydrogen to fuse in the core.
What happens to the Sun at the end
The Sun does not have enough mass to explode as a supernova. It will expand into a red giant, then lose its outer layers and become a white dwarf. It will not become a black hole. Only stars much more massive than the Sun explode as supernovae. For a Sun-like star, the final stages are red giant, then white dwarf.
Describing the life cycle for marks
For a six-mark description, name every stage in order and explain what happens at each one. Keep the sequence clear, from the cloud of gas and dust to the cooling white dwarf.