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P3 4 Summary
Stars and space
Corel 768 (NT)
AQA Science © Nelson Thornes Ltd 2006
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P3 4 Summary
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
AQA Science © Nelson Thornes Ltd 2006
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P3 4 Summary
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!
AQA Science © Nelson Thornes Ltd 2006
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P3 4 Summary
… 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.
AQA Science © Nelson Thornes Ltd 2006
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P3 4 Summary
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.
AQA Science © Nelson Thornes Ltd 2006
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P3 4 Summary
How were the chemical
elements formed?
Higher
• 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.
AQA Science © Nelson Thornes Ltd 2006
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