Explain why a massive star ends its life cycle differently to a star of similar size to the Sun.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Stars form from nebulae and spend most of their lives as main sequence stars. When a star runs out of hydrogen to fuse, it begins the final stages of its life cycle. The path it follows depends on its size.
Model answer (4 marks)
A Sun‑sized star runs out of hydrogen in its core, so the core contracts and heats until helium fusion begins. The outer layers expand and cool, forming a red giant, and after the helium is exhausted the core collapses and the star sheds its envelope, leaving a hot core that cools into a white dwarf.
A massive star, however, can fuse elements up to iron. When iron accumulates, no further energy can be gained from fusion, so the core collapses rapidly. The collapse is halted by neutron degeneracy pressure, causing a rebound that ejects the outer layers in a supernova. The remnant core is either a neutron star or, if massive enough, a black hole.
A massive star, however, can fuse elements up to iron. When iron accumulates, no further energy can be gained from fusion, so the core collapses rapidly. The collapse is halted by neutron degeneracy pressure, causing a rebound that ejects the outer layers in a supernova. The remnant core is either a neutron star or, if massive enough, a black hole.
Examiner tips
- Use the word "collapse" to link fusion end to supernova
- Mention iron fusion as the stopping point
- Show the sequence: fusion → collapse → supernova → remnant
Common mistakes
- Confusing a Sun‑sized star with a massive star’s evolution
- Forgetting that the supernova is due to core collapse, not just mass
- Not specifying that the remnant can be a neutron star or black hole
Mark scheme (4 marks)
- A star similar in size to the Sun expands into a red giant (when hydrogen runs out / heavier elements are fused)
- A Sun-sized star eventually contracts and cools to form a white dwarf
- A massive star undergoes a supernova (because it is too massive to remain stable after fusion reactions end / core collapses and rebounds)
- After a supernova, what remains is either a neutron star or a black hole (depending on the mass of the remnant)
Related
- All Edexcel GCSE Physics (1PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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