AQA GCSE Physics Foundation (8463), Foundation tier · Space physics › Solar system, orbits and satellites
Practise The life cycle of a star. 8 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
How a star changes during its life, why the path it follows depends on its size, and how fusion in stars and supernovae produces the chemical elements. Expect flow charts with missing stages, 'describe' and 'explain' questions, and 6-mark comparisons of two life cycles. GCSE Physics only, not in Combined Science.
Key facts
Every star: nebula → protostar → main sequence star
About the size of the Sun: → red giant → white dwarf → black dwarf
Much bigger than the Sun: → red super giant → supernova → neutron star or black hole
The size (mass) of a star decides its life cycle
Main sequence: hydrogen fuses into helium
Fusion in red giants and red super giants makes heavier elements (up to iron in the biggest stars)
Elements heavier than iron are produced in a supernova
A supernova distributes the elements throughout the universe
Notes
The start of every star
A nebula (cloud of dust and gas) is pulled together by gravity to form a protostar.
When hydrogen starts to fuse into helium in its core, it becomes a main sequence star.
It stays stable while the inward pull of gravity is balanced by the outward pressure from fusion energy. For a star like the Sun, this lasts billions of years.
What happens next depends on the size (mass) of the star.
Stars about the same size as the Sun
When the hydrogen in the core runs out, the star swells to become a red giant. Helium nuclei fuse to form heavier elements, such as carbon.
The outer layers drift away, leaving a white dwarf: a small, very hot, dense core in which fusion has stopped.
The white dwarf cools and fades until it no longer gives out significant light. It is then a black dwarf.
Stars much bigger than the Sun
diagram
When the hydrogen in the core runs out, the star swells to become a red super giant. Fusion forms heavier and heavier elements, up to iron.
The star then explodes as a supernova.
The core that is left becomes a neutron star (extremely dense) or, for the very biggest stars, a black hole (so dense that not even light can escape its gravity).
The path after the main sequence depends on the mass of the star.
How stars make the elements
Fusion processes in stars produce the naturally occurring elements, building them up from hydrogen.
Main sequence stars: hydrogen nuclei fuse to form helium.
Red giants and red super giants: helium and other light nuclei fuse to form heavier elements, such as carbon and oxygen. In the biggest stars this goes as far as iron.
Elements heavier than iron are produced in a supernova.
The explosion of a supernova spreads the elements throughout the universe. New stars and planets, like the Sun and the Earth, form from clouds of dust and gas containing these elements.
How to answer each type of question
Name the missing stages in a life cycle
1 mark eachGrade 3
Decide first which path it is: a star about the size of the Sun, or one much bigger.
Write out the whole sequence for that path from memory, then match it to the chart.
Use the full names, e.g. 'main sequence star', 'red super giant'.
Example. A star much bigger than the Sun goes through these stages: nebula → protostar → main sequence star → A → B → neutron star Name stages A and B.
Show the model answerHide the model answer
A: red super giant (1) B: supernova (1)
Describe the life cycle of a star like the Sun
3 to 4 marksGrade 5
Start from the point the question asks about, e.g. 'after the main sequence'.
Give each stage in order, and say what triggers the change (the hydrogen in the core running out).
End with the final stage: the black dwarf.
Example. The Sun is a main sequence star. Describe what will happen to the Sun after its main sequence stage.
Show the model answerHide the model answer
When the hydrogen in its core runs out, the Sun will swell to become a red giant (1). It will then become a white dwarf, a small, hot, dense core in which there is no fusion (1). The white dwarf will cool and fade until it gives out no significant light, becoming a black dwarf (1).
Don’t lose marks
Saying the Sun will become a supernova or a black hole. It is not big enough: it will become a white dwarf, then a black dwarf.
Writing 'red giant' for a star much bigger than the Sun. Massive stars become red super giants.
Putting the dwarfs in the wrong order. A white dwarf cools to become a black dwarf, not the other way round.
Saying all elements heavier than helium are made in supernovae. Elements up to iron are made by fusion inside stars; it is the elements heavier than iron that are produced in a supernova.
Leaving out the nebula, protostar or main sequence stage when asked for the whole life cycle.
More tips
Memory tricks
The big star's path has 'super' twice: red super giant, then supernova. The Sun's path has no 'super'.
Sun-sized stars go out quietly, cooling from white dwarf to black dwarf. Massive stars go out with a bang (a supernova).
Iron is the cut-off: elements up to iron are made by fusion inside stars; elements heavier than iron are made in supernovae.
A massive star ends as 'N or B': a neutron star, or a black hole for the very biggest stars.
Exam technique
Use the stage names exactly as the specification does: 'main sequence star', 'red giant', 'red super giant', 'white dwarf', 'black dwarf', 'supernova', 'neutron star', 'black hole'.
In 6-mark answers, stages alone will not reach the top level. Add what happens at each stage: what is being fused, what is balanced, what forms or is scattered.
When asked to compare, write both stars into the same sentence, e.g. 'The Sun becomes a red giant, whereas a much bigger star becomes a red super giant.'
In flow chart questions, look for a stage you already know (e.g. 'supernova' or 'white dwarf') to tell which path it is.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Order the first stages of a star's lifeEvery star starts as a nebula, then becomes a protostar, then a main sequence star.
Grade 4
State what decides a star's life cycleThe size (mass) of the star decides which path it follows after the main sequence.
Grade 4
Describe the life cycle of a Sun-sized starMain sequence star, then red giant, then white dwarf, then black dwarf.
Grade 5
Describe the life cycle of a massive starMain sequence star, then red super giant, then supernova, then neutron star or black hole.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
The Sun is a main sequence star. Which element is fused in the core of a main sequence star?
Hydrogen
Gold is an element that is heavier than iron. Where was the gold found on the Earth produced?
In a supernova
State what eventually happens to a white dwarf.
It slowly cools and becomes a black dwarf.
Name the heaviest element that can be produced by nuclear fusion inside a normal star (before it explodes).
Iron
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
The Sun is a main sequence star.
(a) What will the Sun become after its red giant stage? Tick (✓) one box.[1]
A black hole
A neutron star
A supernova
A white dwarf
(b) Which element is fused in the core of a main sequence star?[1]
(c) Which element is produced by this fusion?[1]
(d) Elements heavier than iron are produced in one stage of the life cycle of a massive star. Name this stage.[1]
Show the answer and mark scheme
(a)Answer: A white dwarf
(b)Answer: Hydrogen
hydrogen
(c)Answer: Helium
helium
(d)Answer: Supernova
supernova
Question 2Medium6 marks
The life cycle of a star depends on its size.
(a) Describe how the life cycle of a star much bigger than the Sun is different from the life cycle of the Sun, after the main sequence stage.[4]
(b) Explain why a white dwarf eventually becomes a black dwarf.[2]
Show the answer and mark scheme
(a)Answer: Sun: red giant → white dwarf → black dwarf. Much bigger star: red super giant → supernova → neutron star or black hole.
the Sun will become a red giant, but a much bigger star becomes a red super giant
the Sun will become a white dwarf
a much bigger star explodes as a supernova
a much bigger star ends as a neutron star or a black hole, whereas the Sun’s white dwarf cools to become a black dwarf
(b)Answer: With no fusion, it cools as it radiates until it no longer emits visible light.
there is no fusion in a white dwarf, so it cools down as it emits radiation
eventually it is too cool to emit (significant) visible light