# A star spends most of its life as a main sequence star. Describe the life cycle of a star that has a similar mass to the Sun, from the main sequence stage until it reaches its final state.

> WJEC A-Level Physics (Wales) — 6.3 Stellar evolution and cosmology (A-Level only) · Describe · 5 marks

## Mark scheme (5 marks)

1. A main sequence star is in a state of balance/equilibrium between the inward force of gravity and the outward radiation/thermal pressure from nuclear fusion
2. When hydrogen fuel runs out the core contracts/collapses and the outer layers expand, forming a red giant
3. The red giant undergoes helium fusion / fuses heavier elements in its core
4. The outer layers are ejected/shed to form a planetary nebula
5. The remaining core becomes a white dwarf, which gradually cools over time

## Key terms

- [main sequence](https://www.gradenine.co.uk/glossary/main-sequence)

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-star-spends-most-of-its-087d9ef7) · Published by Druglandscape Ltd.