Stars

• GCSE Physics Unit 2
• Types of stars


  • Large mass star
  • Low mass star
  • e.g. The Sun
• Hertzsprung-Russell diagram (H-R diagram)


  A way of presenting a lot of information about stars, it shows their size, temperature, colour, luminosity (brightness) and they are grouped into the different stages of the star's life cycle
• SUPERGIANTS


  • Lifetime: 107 yrs
  • Mass: 30 MSun
  • Radius: 1 Solar Radius
• MAIN SEQUENCE


  • Lifetime: 108 yrs
  • Mass: 10 MSun
• GIANTS


  • Lifetime: 109 yrs
  • Mass: 6 MSun
• WHITE DWARFS


  • Lifetime: 1010 yrs
  • Mass: 0.3 MSun
  • Radius: 0.01 Solar Radius
• Stars


  • Depend on fusion of elements to release their energy
  • Stability depends on gravitational force acting inwards and radiation and gas pressure acting outwards
• Star formation


  1. Clouds of gas, hydrogen and helium, and dust form

  2. Gravity collects the cloud together and it heats up as it is compressed

  3. Hydrogen fuses to form helium, creating radiation and gas pressure to balance gravitational forces
• Main sequence star life cycle

  1. Hydrogen fuel runs out

  2. Star begins to fuse helium into larger elements (e.g. iron)

  3. Increased gas and radiation pressure causes star to expand into a Supergiant
• Supergiant star life cycle

  1. Helium fuel runs out, reaction slows

  2. Star becomes very unstable and explodes in a supernova, throwing gases and dust out into space

  3. High pressure and temperature in supernova causes fusion of heaviest elements

  4. Remaining matter collapses due to gravitational force to form a Neutron star or Black hole
• Low mass star life cycle

  1. Hydrogen fuel runs out, star begins to fuse helium into larger elements (e.g. carbon)

  2. Increased gas and radiation pressure causes star to expand into a Red giant

  3. Helium fuel runs out, gas and radiation pressure decrease

  4. Star shrinks to form a White dwarf