Explain how the life cycle of a star much more massive than the Sun differs from that of a star similar in size to the Sun, starting from when each star leaves the main sequence.

Edexcel A-Level Physics (9PH0) — 7.3 Magnetic fields and electromagnetic induction · Explain · 5 marks · View as Markdown

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

Stars spend most of their lives as main sequence stars. When hydrogen fuel runs out, the subsequent stages depend on the mass of the star.

Model answer (5 marks)

Both stars expand when core hydrogen is exhausted. A Sun‑like star becomes a red giant, then loses its envelope and forms a white dwarf. A massive star becomes a super‑giant, fuses progressively heavier elements up to iron, then undergoes a core‑collapse supernova. The supernova leaves a neutron star or black hole.

1. Expansion after core H exhaustion
2. Sun‑like star → red giant → white dwarf
3. Massive star → super‑giant → core‑collapse supernova
4. Supernova produces neutron star or black hole

Examiner tips

  • Use the word ‘expansion’ to link the two stages; mention red giant vs super‑giant. Include the final remnants. Keep each point short and to the mark scheme.
  • Show the sequence clearly: expansion → fusion stages → final remnant.
  • Use the exact terms: red giant, white dwarf, super‑giant, supernova, neutron star, black hole.
  • Avoid extra detail such as planetary nebulae unless asked.

Mark scheme (5 marks)

  1. Both types of star first expand / swell when hydrogen runs out
  2. A Sun-like star expands into a red giant (whereas a massive star becomes a supergiant / undergoes more extensive fusion of heavier elements)
  3. A massive star undergoes a supernova (violent explosion) whereas a Sun-like star does not
  4. A Sun-like star ends as a white dwarf (contracts and cools)
  5. A massive star ends as a neutron star or black hole (after the supernova)

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