Life Cycle of a Star

• What is present in a galaxy?

  Dust and gas cloud
• What draws the gas and dust particles to be drawn together?

  Gravitational attraction
• The cloud becomes more concentrated, as the particles get closer
• The temperature and pressure of the cloud increases as the particles get pushed so close together
• Eventually the pressure gets so great that the gas/dust particles are able to fuse together:

  • Fusion occurs as the light nuclei fuse together to form helium nuclei
  • This creates a large amount of energy
  • This release opposes the collapsing of the cloud due to gravity
  • an equilibrium forms where the energy released due to fusion balances the pressure of gravitational collapse
  • This means a star has now formed
• Eventually the star runs out of gas to fuse, this means it is nto in equilibrium so it collapses
• If a massive star runs out of gas:

  The star will collapse, increasing the pressure + temperature of the core, meaning heavier elements can fuse. Once all the fusion has happened, it is too massive to be stable, so the star collapses, rebounds on its centre and produces a supernova. What remains is either a neutron star or black hole
• If a normal-sized star runs out of gas to fuse:

  Star collapses, and produces a planetary nebula, which is a lower scale supernova. A white dwarf remains.