The life cycle of a star

    AQA
    GCSE

    The life cycle of a star is determined fundamentally by its initial mass, initiating with the gravitational collapse of a nebula into a protostar. During the stable main sequence phase, candidates must explain the equilibrium between inward gravitational attraction and outward radiation pressure arising from the nuclear fusion of hydrogen. The curriculum requires differentiation between the evolution of solar-mass stars—progressing to red giants and white dwarfs—and massive stars, which evolve into red supergiants and culminate in supernovae, leaving neutron stars or black holes. Mastery involves linking these processes to nucleosynthesis and the cosmic dissemination of elements heavier than iron.

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    Objectives
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    Exam Tips
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    Pitfalls
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    Key Terms
    4
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that gravity pulls dust and gas together in a nebula to form a protostar
    • Credit responses that explain main sequence stability as a balance between inward gravitational attraction and outward radiation pressure from nuclear fusion
    • Award 1 mark for identifying that elements heavier than iron are produced only during a supernova explosion
    • Candidates must link the final stage to mass: stars much more massive than the Sun become neutron stars or black holes, while Sun-like stars become black dwarfs

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You have listed the stages correctly, but you need to explain *why* the star expands into a Red Giant (imbalance of forces)"
    • "Be careful with the endpoint for the Sun — remember it is not massive enough to cause a supernova"
    • "Excellent use of 'equilibrium' — now ensure you specify which two forces are balanced"
    • "You mentioned heavy elements; make sure to specify that those heavier than iron require the energy of a supernova"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that gravity pulls dust and gas together in a nebula to form a protostar
    • Credit responses that explain main sequence stability as a balance between inward gravitational attraction and outward radiation pressure from nuclear fusion
    • Award 1 mark for identifying that elements heavier than iron are produced only during a supernova explosion
    • Candidates must link the final stage to mass: stars much more massive than the Sun become neutron stars or black holes, while Sun-like stars become black dwarfs

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When describing the main sequence, explicitly use the terms 'gravitational collapse' and 'radiation pressure' to define the equilibrium
    • 💡Memorise the two distinct pathways: 'Sun-like' (Red Giant → White Dwarf) vs 'Massive' (Red Super Giant → Supernova)
    • 💡For questions on elements, clearly distinguish that fusion creates elements up to iron, but supernovae are required for anything heavier

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Stating that the Sun will eventually become a black hole (it lacks sufficient mass and will become a black dwarf)
    • Confusing the direction of forces: incorrectly stating gravity pushes outwards or pressure pulls inwards
    • Believing fusion ceases entirely when a star leaves the main sequence (fusion of helium and heavier elements continues in Red Giants/Super Giants)
    • Asserting that elements heavier than iron are formed during the main sequence stage

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

    Describe
    Explain
    State
    Compare
    Predict

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