The Life Cycle of Larger Stars (Edexcel IGCSE Science (Double Award)) : Revision Note

The life cycle of larger stars

• After the main sequence, a high-mass star finishes its life cycle in the following evolutionary stages:

Red supergiant → supernova → neutron star (or black hole)

• The key differences between a lower mass and higher mass star at this stage are:

  • A higher mass star will stay on the main sequence for a shorter time before it becomes a red supergiant

  • A lower mass star fuses helium into heavy elements, such as carbon, whereas a higher mass star fuses helium into even heavier elements, such as iron

Red supergiant

• After several million years, the hydrogen causing the fusion reactions in the star will begin to run out

• Once this happens, the fusion reactions in the core will start to die down

• The star will begin to fuse helium which causes the outer part of the star to expand

• As the star expands, its surface cools and it becomes a red supergiant

Supernova

• Once the fusion reactions inside the red supergiant cannot continue, the core of the star will collapse suddenly and cause a gigantic explosion called a supernova

• At the centre of this explosion, a dense body called a neutron star will form

• The outer remnants of the star are ejected into space forming new clouds of dust and gas (nebula)
  

  • The heaviest elements are formed during a supernova, and these are ejected into space

  • These nebulae may form new planetary systems

Neutron star (or black hole)

• In the case of the most massive stars, the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole

• A black hole is an extremely dense point in space that not even light can escape from

The life cycle of a high-mass star

The life cycle of a star much larger than our Sun