1. AQA Science © Nelson Thornes Ltd 2006 1 P3 4 Summary Stars and space Corel 768 (NT)

2. P3 4 Summary AQA Science © Nelson Thornes Ltd 2006 2 What are galaxies? The Big Bang which created the universe was about 13 thousand million years ago. As the Universe expanded, it cooled and uncharged atoms formed. The force of gravity pulled matter into galaxies and stars. SPL NOAO/AURA/NSF

3. P3 4 Summary AQA Science © Nelson Thornes Ltd 2006 3 How are stars born …? Stars form out of clouds of dust and gas. Particles gather under gravity to form a protostar. The protostar becomes denser and hotter. If it reaches a point where hydrogen and other atoms fuse – huge amounts of energy (including light) are released and a star is born!

4. P3 4 Summary AQA Science © Nelson Thornes Ltd 2006 4 … And how do stars die? When the supply of hydrogen nuclei runs out, the star swells. As it swells, it cools and turns red – a red giant. When all the light elements in the core have fused, fusion stops. The star collapses on itself and heats up to become a white dwarf. Smaller stars (like our Sun) then fade out and go cold.

5. P3 4 Summary AQA Science © Nelson Thornes Ltd 2006 5 What happens to bigger stars? High-mass stars continue to collapse beyond the white dwarf stage until there is a massive explosion outwards again – a supernova. The supernova compresses the core of the star into a very dense neutron star. If the neutron star is massive enough it becomes a black hole.

6. P3 4 Summary AQA Science © Nelson Thornes Ltd 2006 6 How were the chemical elements formed? Light elements – up to and including iron – are formed as a result of the fusion of nuclei in stars. Heavy elements are formed when a massive, ageing star collapses and then explodes as a supernova. Higher