The Life Cycle of a Star

1
The Life Cycle of a Star

• Upper Fifth Physics

2
In The Beginning

• Lots of gas and dust
• All this stuff gravitationally attracted
• Click picture for full news story

3
War between gravity and pressure

• If the mass of gas is large enough, then the
  gravitational attraction of the particles will
  overcome the pressure and the cloud will contract

4
Ignition!

• As the cloud contracts, GPE is converted into KE.
• Temperature of cloud is related to the average KE
  of the molecules.
• Increase in KE means an increase in
  temperature.
• If temperature exceeds 15 million K, hydrogen
  fuses into helium and we have ignition!

5
Just keep glowing

• Star continues to glow as long as there is
  sufficient hydrogen.
• Battle between forces due to gravity and pressure
  continues but is stable.
• Each second, the Sun converts 1 million kg of
  hydrogen in helium

6
Running low on gas

• Helium production continues until hydrogen runs
  out.
• Helium fuses into other nuclei, but the process
  isnt as efficient.
• What happens next depends on the original mass of
  the star (click on a button)

Great Links
Little Star
Big Star
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Little Star

• Hydrogen cloud around hot central core drifts off
• As last of hydrogen drifts off, big wind comes
  from surface of core
• Wind distorts hydrogen cloud.
• We have a planetary nebula surrounding a white
  dwarf
• White dwarf cools and fades away

Return to Running Low on Gas
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Big Star

• Star burns helium to other elements, which in
  turn can be fuses into heavier elements still.

9
Large pop!

• Iron doesnt burn so eventually the fusion stops!
• There is nothing to stop the gravitational pull
  of the nuclei on each other.
• Iron core collapses in a second.
• Resulting explosion is a supernova, visible
  between galaxies.
• During this explosion, heavier elements are made
  (all elements in universe heavier than iron
  originally came from supernovae including those
  inside you!

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Whats left?

• If the stars core was small then a small
  spinning lump of neutrons called a neutron star
  is left.
• If the stars core was large then a black hole
  is left.

Back to Running out of Gas
11
Great Links

• NASA for a more in depth description
• More pretty pictures of
• Stellar births
• Stellar deaths
• The science of black holes (odd stuff happens
  there)