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

Supernovae

  • 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.
Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top