# Describe the life cycle of a star similar in size to the Sun, starting from a nebula and ending at its final stage.

> OCR GCSE Physics A: Gateway Science (J249) — P6.3 Astronomy · Describe · 4 marks

> Scientists study stars at different stages of their life cycles to understand how our own Sun formed and how it will eventually change. By observing many different stars, astronomers can piece together the sequence of stages a star like the Sun passes through during its lifetime.

## Mark scheme (4 marks)

1. A nebula (cloud of dust and gas) is pulled together by gravitational attraction to form a protostar
2. The protostar becomes hot enough for hydrogen nuclei to undergo fusion, forming a main sequence star where gravitational forces and outward pressure are balanced
3. When hydrogen runs out, the star expands to form a red giant (as larger nuclei are produced by fusion)
4. The red giant eventually collapses and sheds its outer layers to leave behind a white dwarf as the final stage

## Key terms

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

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-the-life-cycle-of-a-67d38b3a) · Published by Druglandscape Ltd.