Astrophysics

• • Nuclear fusion is when small nuclei fuse together to make heavier nuclei.  
  • Lots of energy is released during fusion. 
  • Fusion can only happen at very high temperatures and pressures 
  • If the temperatures/pressures aren't high enough, the positive nuclei repel each other 
  • These conditions are found in stars 
• A nebula is a cloud of dust and gas
• A protostar is formed from gravity pulling these particles together. As they move inwards their gravitational potential energy is concerted into heat and a protostar is formed
• For a small - medium star:

  main sequence star --> red giant --> white dwarf --> black dwarf
• For a large star:

  main sequence star --> red super giant --> supernova --> neutron star
• For a massive star:

  main sequence --> red super giant --> supernova --> black hole
• The forces of attraction pulling the particles inwards are balanced by expansion forces due to nuclear fusion reactions and the high temperature. 

   

  Stars are basically nuclear reactors that use hydrogen as a fuel.  During its main sequence a star will release energy by converting hydrogen and helium (light elements) into heavier elements and this is why the universe now contains a number of heavier elements.