Describe the sequence of events that leads to the formation of a neutron star, beginning from when a massive star runs out of hydrogen fuel.

Cambridge International IGCSE Physics (0625) — 6.2 Stars and the Universe · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

The massive star runs out of hydrogen and its core collapses, causing the outer layers to expand and the star to become a red supergiant.
The core collapse triggers a core‑collapse supernova, blowing the outer layers into space.
The supernova leaves behind a hot, dense remnant and a surrounding nebula of expelled material.
The remnant collapses further to form a neutron star at the centre of the nebula.

Examiner tips

  • Use the sequence: core collapse → red supergiant → supernova → nebula + neutron star.
  • Mention the core collapse as the trigger for the supernova.
  • Keep the answer concise – 4 marks, one point per sentence.
  • Use correct terminology: core collapse, supernova, neutron star, nebula.

Common mistakes

  • Confusing the red supergiant phase with the supernova; the star expands before exploding.
  • Omitting the nebula or describing it incorrectly.
  • Using vague terms like ‘big explosion’ instead of ‘core‑collapse supernova’.

Mark scheme (4 marks)

  1. The massive star expands to form a red supergiant (when hydrogen fuel runs out / outward force exceeds gravitational attraction)
  2. The red supergiant explodes as a supernova
  3. The supernova creates / leaves behind a nebula (containing hydrogen and heavier elements)
  4. A neutron star is left at the centre (of the nebula / after the supernova)

Key terms in this question

neutron star

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