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AQA GCSE Physics Unit 3
The life history of stars…read more

Slide 2

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A Star is Born
· Originally, Space was just a massive cloud of dust and hydrogen gas.
· The gravity of the dust particles pulled them together.
· The "clump" was bigger, so it had a larger force of gravity acting on it,
and attracted more dust and gases.
· This is called a proton star.
Star!…read more

Slide 3

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Stability and Nuclear Fusion
· The star still has a gravitational force acting towards its centre.
· The centre has enough heat and pressure to fuse hydrogen nuclei together to
make helium nuclei.
· Fusion releases energy, creating radiation pressure, which acts outwards from
the centre.
· The star is stable because the gravitational force and the radiation pressure are
balanced, and there is sufficient hydrogen to last a long time.
Radiation Pressure…read more

Slide 4

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The Red Giant
· When the star uses up all the hydrogen, it begins to fuse
helium cells to make much heavier elements.
· However, these elements are no heavier than iron.
· This means the radiation pressure increases, so the forces
are unbalanced and the star expands to a red giant.
Radiation Pressure
Helium nuclei fusing together
to make heavy elements.
Hydrogen nuclei fusing
together to make helium.
Hydrogen.…read more

Slide 5

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The White Dwarf
· As the star grows, its mass increases, and therefore its gravity does as well.
· Also, it has fused all the elements it has, so it has no radiation pressure.
· Consequently, it reaches the stage where its gravitational force is greater than its radiation
· This causes it to go in on itself, and become a white dwarf.
· The star is white because it is hotter than before, and white is a hotter colour than red.
Radiation Pressure…read more

Slide 6

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What happens next?
· This depends on how massive the star is.
· Either the star has
- A small mass (including our Sun)
- A large mass (much bigger than our Sun).
· Click on the links to view each separate
ending.…read more

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