life cycle

• The life cycle for a particular star depends on whether

  • it is about the same size as the Sun
  • it is far greater than the Sun in size

  
• 1. dust and clouds form a

  nebula

  
• • The gravitational attraction between the

  gas/dust particles push them together

  
• 3. The cloud becomes more concentrated, 


  as the particles get closer

  
• The temperature and pressure of the cloud

  increases as friction between the two force increases

  
• as the pressure increases the particles begin to fuse together

  
• Nebula

  Cloud of dust and gas
• Star formation

  1. Gravity causes cloud of dust and gas to collapse

  2. As particles move faster, temperature rises to millions of degrees Celsius

  3. This early stage is called a protostar
• Nuclear fusion

  Hydrogen nuclei join together to form helium nuclei
• Main sequence star

  • Hydrogen nuclei fuse together to make larger nuclei such as helium
  • Releases a huge amount of energy
  • Can stay in this stage for a very long time
• Transition from main sequence star

  1. Hydrogen begins to run out

  2. Outward force from fusion energy is less than inward force from gravity

  3. Star collapses inwards

  4. Temperature increases

  5. Helium nuclei fuse to create heavier elements

  6. Star expands to form a red giant
• Red giant

  • Stops fusing helium
  • Shrinks and forms a white dwarf
  • White dwarf gradually cools down and stops releasing energy, forming a black dwarf
• Transition of larger stars from main sequence

  1. Run out of hydrogen

  2. Expand into red supergiants

  3. Helium nuclei fuse to produce heavier elements

  4. Nuclear fusion cannot make elements heavier than iron
• Supernova

  • Explosion of a red supergiant
  • Temperature is high enough to produce elements heavier than iron
  • Distributes these heavy elements throughout the universe
• Remnants of supernova

  • Can form a neutron star (densely packed neutrons)
  • Can form a black hole (large gravity that even light cannot escape)
• Elements heavier than iron are only produced in a supernova