This is an overview of the life cycle of a star and other relavent information


Stage 1

  • They begin as clouds of dust and gas
  • Denser clumps contract under gravity
  • As this happens the temperature increases
  • Eventually the temperature at the centre reaches a few million degrees and hydrogen nuclei fuse together to form helium
  • This releases large energy (nuclear fusion), and provides enough pressure to stop gravitational collapse
  • Star has now reached the main sequence
  • It will stay there in a long stable phase, relatively unchanged
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Stage 2

  • Main sequence stars become red giants when they run out of fuel
  • When the hydrogen in the core runs out fusion stops - outward pressure stops
  • Core contracts, heats up under weight of the star, and then gets hot enough and dense enough for helium to fuse
  • This releases huge energy, causing the star to expand into RED GIANT - RED SUPERGIANT
  • They have a high luminosity, low surface temperature - large surface area
  • This is due to the Stefan - Boltzmann law
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Stage 3a

  • Low mass stars like the Sun will form white dwarfs
  • Once all helium has fused, low mass stars will collapse under their own weight
  • The core will not get hot enough for more fusion - just continue to contract
  • Once Earth size, electrons will exert enough pressure to stop further collapse
  • As the core contracts the outer layers become more and more unstable
  • The star pulsates and ejects its outer layers into space as planetry nebula
  • The star is a hot, dense solid called a WHITE DWARF
  • They have a low luminosity and high surface temperature
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Stage 3b

  • High mass stars have a shorter life and more exiting death
  • Large mass - lots of fuel - use it more quickly - less time in main sequence
  • They will keep fusisng elements untill they are just left with Iron
  • When it runs out of fuel - contracts to a white dwarf
  • If its massive enough (1.4 mass of sun), it keeps contracting
  • The electrons get squashed onto the atomic nuclei - forming neutrons and neutrinos
  • Core collapses to become a neutron star- which outer layers fall on to
  • When the outer layers hit the surface they rebound setting up huge shockwaves, ripping the star apart and causing a supernova
  • The light of which can briefly outshine an entire galaxy
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Jacob Freshwater


thanks mate

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