Describe the stages in the life cycle of a star that has a similar mass to the Sun, beginning from a nebula and ending as a white dwarf.

Pearson Edexcel International GCSE Physics (4PH1) — 8.2 Stellar evolution · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

A nebula is a cloud of dust and gas that is pulled together by gravity.
The collapsing cloud forms a protostar, where temperature and pressure become high enough for nuclear fusion of hydrogen to begin.
The star becomes a main‑sequence star, where the inward gravitational force is balanced by the outward pressure from nuclear fusion.
When hydrogen is used up, the star expands to form a red giant, then contracts under gravity and cools to form a white dwarf.

Examiner tips

  • Use the exact sequence: nebula → protostar → main‑sequence → red giant → white dwarf. Mention gravity vs. fusion balance. Keep answer concise, 4 points total.

Common mistakes

  • Mixing up the order of stages. Forgetting to mention the balance of forces in the main‑sequence stage. Using vague terms like ‘star’ instead of specific stages.

Mark scheme (4 marks)

  1. A nebula is a cloud of dust and gas that is pulled together by gravity / gravitational attraction
  2. The collapsing cloud forms a protostar, where temperature and pressure become high enough for nuclear fusion of hydrogen to begin
  3. The star becomes a main sequence star, where the inward gravitational force is balanced by the outward pressure from nuclear fusion
  4. When hydrogen is used up, the star expands to form a red giant, then contracts under gravity and cools to form a white dwarf

Key terms in this question

nebula · white dwarf

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