The Life Cycle of a Star
Build confidence in The Life Cycle of a Star for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) physics topic: stars form from clouds of gas and dust, and their final stages depend on their mass, from white dwarfs to black holes.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
A star forms when enough dust and gas from space is pulled together by gravitational attraction, forming a protostar. This is a Triple-only topic.
As the mass falls together, the temperature rises. When it is high enough, hydrogen nuclei fuse to form helium nuclei, releasing energy. This keeps the core hot, and the star enters a long stable period called the main sequence.
During the main sequence the forces are balanced: the outward force from fusion energy balances the inward force of gravitational attraction. What happens next depends on the star's mass. A star like the Sun becomes a red giant, then a white dwarf. A much more massive star becomes a red supergiant, explodes as a supernova, and leaves a neutron star or a black hole.
Revision notes
Formation and the main sequence
Dust and gas are pulled together by gravitational attraction, forming a protostar. The temperature rises as the mass falls together.
When hot enough, hydrogen nuclei fuse to form helium, releasing energy. This begins the main sequence, a long period of stability.
Why the main sequence is stable
The forces within the star are balanced.
The outward force caused by the energy released in fusion balances the inward force of gravitational attraction. This equilibrium keeps the star's size constant for billions of years.
The two possible endings
A star about the size of the Sun: red giant, then white dwarf.
A star much more massive than the Sun: red supergiant, then supernova explosion, leaving either a neutron star or, if massive enough, a black hole. Fusion in stars produces the naturally occurring elements, and a supernova distributes them through the universe.
Key points
- Stars form from dust and gas pulled by gravity.
- A protostar heats as its mass falls together.
- Hydrogen fuses to helium, releasing energy.
- Main sequence forces are balanced.
- Sun-sized stars become red giants then white dwarfs.
- Massive stars explode as supernovae.
Worked examples
Example 1
Explain why a main sequence star remains stable for a long period. [3 marks]
Model answer
Energy released by nuclear fusion in the core produces an outward force (1 mark). This balances the inward force of gravitational attraction (1 mark), so the forces are balanced and the star's size remains constant (1 mark).
Example 2
Describe the life cycle of a star about the same size as the Sun after the main sequence. [2 marks]
Model answer
It expands to become a red giant (1 mark), and then contracts to become a white dwarf (1 mark).
Example 3
Explain how elements heavier than iron are distributed through the universe. [2 marks]
Model answer
They are produced in a supernova explosion (1 mark), which distributes the elements throughout the universe (1 mark).
Common mistakes
Saying the main sequence has no forces acting.
The forces are balanced, not absent.
Giving the same ending for all stars.
It depends on mass: Sun-sized stars and massive stars end differently.
Confusing red giant and red supergiant.
Red giant follows a Sun-sized star; red supergiant follows a massive one.
Saying a white dwarf explodes.
It is the massive star route that ends in a supernova.
Exam tips
- Explain main sequence stability through balanced forces.
- Learn both life cycle routes separately by mass.
- Name the stages in the correct order.
- Remember this is a Triple-only topic.
Key terms
- Protostar
- The early stage of a star forming from dust and gas.
- Main sequence
- The long stable period of a star's life.
- Red giant
- The stage following the main sequence for a Sun-sized star.
- Supernova
- The explosion ending a massive star's life.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.