Production of Elements (Oxford AQA IGCSE Combined Science Double Award)

Production of Elements

• Fusion reactions in stars are their source of energy

  • They produce all of the naturally occurring elements in the Universe

  • These elements may be distributed throughout the Universe by the explosion of a massive star (supernova) at the end of its life

• For main sequence stars with a mass larger than that of our Sun:

  • Hydrogen nuclei combine in nuclear fusion reactions to produce helium nuclei, releasing lots of energy in the process

  • Stars maintain their energy output for millions of years because of the large amounts of hydrogen available

  • Once all of the hydrogen has reacted, fusion slows and the star expands becoming a red supergiant

  • Helium nuclei are then fused to form carbon

  • Further fusion processes take place in which heavier nuclei are formed such as nitrogen and oxygen

  • Heavier elements up to iron are also formed

Forces on a main sequence star

• Once the fusion reactions inside the red supergiant cannot continue, the core of the star will collapse suddenly

• The outer layers are blown away in a gigantic explosion 

  • This is called a supernova

  • The temperatures in the explosion are so high that the heavier nuclei can fuse to create all the naturally occurring elements in the Universe

    • All elements heavier than iron are created in supernovae

  • The explosion disperses these elements out into space

• The early Universe contained only hydrogen because fusion is needed to create heavier nuclei

  • Before stars formed there was no fusion

Forces on a red supergiant