8.4.3 life cycle of stars

• All stars fuse hydrogen nuclei into helium in nuclear fusion
• Large stars

  • larger stars fuse hydrogen nuclei into lithium and other light metals
• Supernovae

  • a supernova produces enough energy for hydrogen nuclei to form elements heavier than iron
• All of the naturally occurring elements are produced by nuclear fusion in stars.
• Life Cycle of a Star like the Sun

  • gravity pulls gas and dust together to form a protostar
  • main sequence star formed, powered by nuclear fusion
  • the star expands, becoming a red giant
  • star cools and collapses inwards, forming a white dwarf
  • star completely cools and becomes a black dwarf, no light or heat emitted anymore
• A supernova produces enough energy for hydrogen nuclei to form elements heavier than iron.
• A star begins when a nebula (a cloud of dust and gas) collapses under gravity to form a protostar
• Life Cycle of a Large Star

  • gravity pulls gas and dust together to form a protostar
  • main sequence star formed, powered by nuclear fusion
  • the star expands, becoming a red supergiant
  • the star explodes in a supernova
  • the supernova leaves behind either a black hole or a neutron star