The star life cycle

• 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


  • Nuclear fusion releases a huge amount of energy
  • Stars can stay in the main sequence for a very long time
• Lifecycle of a star about the same size as the Sun


  1. Hydrogen nuclei fuse together to make helium

  2. Hydrogen begins to run out, outward force from fusion is less than inward force of gravity, causing star to collapse inwards

  3. Collapse causes temperature to increase, helium nuclei fuse to create heavier elements

  4. Star expands to form a red giant

  5. Red giant stops fusing helium, star shrinks and forms a white dwarf

  6. White dwarf gradually cools down and forms a black dwarf
• Lifecycle of a much larger star than the Sun

  1. Star leaves main-sequence stage and expands into a red supergiant

  2. Helium nuclei fuse to produce heavier elements

  3. Nuclear fusion cannot make elements heavier than iron

  4. Star stops nuclear fusion and explodes in a supernova

  5. Supernova produces elements heavier than iron

  6. Supernova explosion distributes these heavy elements throughout the universe

  7. Remains of star can form a neutron star or a black hole
• Elements heavier than iron are only produced in a supernova
• Neutron star consists of neutrons densely packed together
• Black hole has such a large gravity that not even light can escape