# Explain the full life cycle of a star that is similar in size to the Sun, starting from a nebula.

> Edexcel A-Level Physics (9PH0) — 7.2 Capacitors · Explain · 5 marks

## Mark scheme (5 marks)

1. A nebula is a cloud of dust and gas that is pulled together by gravitational attraction, forming a protostar.
2. In the protostar, temperature and pressure increase until hydrogen nuclei undergo fusion to form helium, releasing energy — the star enters the main sequence.
3. The star remains stable (on the main sequence) because the outward pressure from fusion balances the inward gravitational force.
4. When hydrogen runs out, the star expands to form a red giant, where heavier elements are produced by fusion.
5. Once fusion reactions end, the star contracts under gravity and cools to form a white dwarf.

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-the-full-life-cycle-of-36b74b90) · Published by Druglandscape Ltd.