AQA GCSE Physics

Revision Notes

8.1.5 The Life Cycle of Larger Stars

Larger Stars

  • A large star is one which is bigger than the Sun
  • Stars that are larger than the Sun have much shorter lifespans – in the region of hundreds of millions of years (instead of billions)
    • This is because they burn through the fuel in nuclear fusion much quicker than smaller stars
  • The life cycle of a star bigger than the Sun starts in the same way as a solar mass star

1. Nebula

  • All stars form from a giant cloud of hydrogen gas and dust called a nebula

2. Protostar

  • The force of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas, known as a protostar
  • As the particles are pulled closer together the density of the protostar will increase
    • This will result in more frequent collisions between the particles which causes the temperature to increase

3. Main Sequence Star

  • Once the protostar becomes hot enough, nuclear fusion  reactions occur within its core
    • The hydrogen nuclei will fuse to form helium nuclei
    • Every fusion reaction releases heat (and light) energy which keeps the core hot

4. Red Supergiant

  • Eventually, the main sequence star will reach a stage when it starts to run out of hydrogen gas in its core
  • Once this happens, the fusion reactions in the core will start to die down
  • This causes the core to shrink and heat up
    • The core will shrink because the inward force due to gravity is greater than the outward force due to the pressure of the expanding gases
  • A new series of fusion reactions will then occur around the core, for example helium nuclei will undergo fusion to form beryllium
  • These fusion reactions will cause the outer part of the star to expand and it will become a super red giant
    • A super red giant is much larger than a red giant

5. Supernova

  • Once the fusion reactions inside the red supergiant finally finish, the core of the star will collapse suddenly causing a gigantic explosion
    • This is called a supernova
  • At the centre of this explosion a dense body, called a neutron star will form
  • The outer remnants of the star will be ejected into space during the supernova explosion, forming a planetary nebula

6. Neutron Star (or Black Hole)

  • In the case of the biggest 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

Lifecycle of Larger Mass Stars, downloadable IGCSE & GCSE Physics revision notes

Lifecycle of a star much larger than our Sun


  • A supernova is a bright and powerful explosion that happens at the end of a massive star’s life
    • It occurs when the star is bigger than the Sun
  • The explosion releases a large amount of energy
  • During a supernova, all of the elements which were produced by the fusion reactions are exploded out along with neutrons
  • The neutrons combine with the elements to form even heavier elements
  • These elements are ejected into the universe by the supernova explosion and form new planets and stars
    • Since Earth contains many heavy elements up to Iron, this is proof that it must have once been made from the remains of a Supernova

Supernova, downloadable IGCSE & GCSE Physics revision notes

A supernova

Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

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