# A star spends most of its life on the main sequence. Explain what is meant by the main sequence and describe the sequence of events that occurs when a star like the Sun eventually leaves the main sequence and reaches its final state.

> Eduqas A-Level Physics — 6.3 Stellar evolution and cosmology (A-Level only) · Explain · 5 marks

> Stars like the Sun are formed from clouds of gas and dust in space. After a long period of stability, they undergo dramatic changes before reaching their final state.

## Mark scheme (5 marks)

1. The main sequence is a stable period/stage in a star's life where nuclear fusion of hydrogen (into helium) provides an outward pressure that balances gravitational collapse
2. When hydrogen in the core runs out, the star expands and cools to become a red giant
3. The outer layers of the red giant are ejected/shed, forming a planetary nebula
4. The remaining hot, dense core becomes a white dwarf
5. The white dwarf gradually cools over time and will eventually become a black dwarf (a cold, dark, non-luminous object)

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Physics](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-star-spends-most-of-its-bc0d464f) · Published by Druglandscape Ltd.