Edexcel IGCSE Physics: Double Science 复习笔记:8.2.3 The Life Cycle of Larger Stars

Edexcel IGCSE Physics: Double Science 复习笔记:8.2.3 The Life Cycle of Larger Stars

The Life Cycle of Larger Stars


  • large star is one that is much larger 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)


  • The life cycle of a star larger 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


  • Thermal expansion from fusion reactions occur within its core and the force of gravity keeps the star in equilibrium
  • At this point, the star is born, and it becomes a main-sequence star
  • During the main sequence, the star is in equilibrium and said to be stable
    • The inward force due to gravity is equal to the outward pressure force which results from the expanding hot gases inside the star



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 a supernova


6. Neutron Star (or Black Hole)

  • At the centre of this explosion a dense body, called a neutron star will form
  • In the case of the largest 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 stars much larger than our Sun



Exam Tip

Make sure you remember the life cycle for a high mass star and ensure you can describe the sequence in a logically structured manner in case a 6 marker comes up in the exam!Ensure you can remember the end stages for a high mass star clearly (red supergiant, supernova, neutron star/black hole) as this is different for a star that is a similar size to the Sun!