Stellar Evolution

• Stage 1 planetary nebula

  • nebula where gas molecules move slowly
  • denser clumps of cloud contact very slowly under gravity
  • gravity forces hydrogen gas to form sphere, protostar
• Process after planetary nebula

  gravity forces hydrogen gas to form sphere, protostar
• Stage 2: protostar

  gravitational attraction takes over and pushes particles together to from a sphere

  as clumps of hydrogen and helium come together the density of area increases, increasing collisions and temperature
• What can be said about the protostar state

  too cold to carry out nuclear fusion process
• What happens to protostar eventually?

  temperature and pressure increase so much, fusion begins
• Stage 3: Main Sequence

  hydrogen fuses together to form helium

  mass before greater than mass after
• What are the 2 forces acting on a main sequence star?

  gravitational attraction and fusion pressure force
• Gravitational force in main sequence

  produced by mass of particle in the star and acts inwards
• Fusion pressure force in main sequence

  produced by products of fusion escaping star
• In which direction do the forces act on main sequence star?

  gravitation inwards and fusion pressure outwards
• What eventually happens in main sequence?

  hydrogren runs out, heavier elements begin to fuse
• Stage 4: Red Giant

  • when all hydrogen is fused into helium, fusion stops
  • temperature of core increases enough to allow for fusion of helium
  • size of star increases pressure > gravity so expansion
• Process after Red Giant

  • fusions stops as there is not enough pressure
  • outer layer drifts
  • white dwarf formed
• What can be said about the core of red giants?

  not large enough to fuse heavier elements so star collapses under force of gravity and shell of helium around is ejected
• Stage 5: white dwarf


  no longer carrying out fusion, emits light as afterglow and core of carbon left
• What is left behind at white dwarf stage?

  core of carbon
• Stage 6: Black Dwarf

  white dwarf cooled down and radiation is lost to space
• When fusion = grav in main sequence

  red super giant
• Stage: Red Super Giant

  • temp of core increases, fusion of helium begins
  • increase in pressure leading to expansion
• What happens after red super giant?

  star fuses to make iron

  when fuel is depleted fusion stops and fusion pressure decreases this allows grav force to act on and implode star into its core
• Stage: Supernova

  explosion distributing all elements produced at red giant to form new nebulae
• What happens at supernova in terms of M

  brief rapid increase in absolute magnitude
• Stage neutron star

  remains of supernova core
• Black hole

  an object with escape velocity greater than speed of light