The life cycle of Stars

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  • The life cycle of Stars
    • Stars initially form from dust and gas. The force of gravity makes the clouds of dust and gas spiral in together to form a protostar.
      • The gravitational energy is converted into heat energy, so the temperature rises. When the temperature gets high enough hydrogen nuclei can undergo nuclear fusion to form helium nuclei and give out massive amounts of heat and light .
        • A star is born.
          • The star enters a long stable period, where the heat created by the nuclear fusion provides an outward pressure to balance the force of gravity pulling everything inwards.
            • It is called a main sequence star.
              • Eventually the hydrogen begins to run out. Heavier elements such as iron are made by nuclear fusion of helium.
                • The star then swells.
                  • If it is a small star it becomes a red giant.
                    • It becomes red because the surface cools.
                      • It then becomes unstable and ejects its outer layer as a planetary nebula.
                        • This leaves a hot dense solid core which is a White dwarf.
                          • It cools down eventually and becomes a black dwarf.
                            • It then disappears.
                  • If it is a big star it becomes a red super giant.
                    • It becomes red because the surface cools.
                      • They then begin to glow brightly again because they undergo more fusion and make elements as heavy as iron, and expand and contract several times


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