Edexcel IGCSE Physics: Double Science 复习笔记:8.2.2 The Life Cycle of Solar Mass Stars

Edexcel IGCSE Physics: Double Science 复习笔记:8.2.2 The Life Cycle of Solar Mass Stars

The Life Cycle of Solar Mass Stars


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 due to fusion 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 Giant

  • After several billion 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
  • This causes the core to shrink and heat up
    • The core will shrink because the inward force due to gravity will become greater than the outward force due to the pressure dies down


  • A new series of reactions will then occur around the core, for example, helium nuclei will undergo fusion to form beryllium
  • As the core shrinks, more reactions will cause the outer part of the star to expand
  • It will become a red giant
    • It is red because the outer surface starts to cool



5. White Dwarf

  • The star will eventually become unstable and eject the outer layer of dust and gas
  • The core which is left behind will collapse completely, due to the pull of gravity, and the star will become a white dwarf
  • The white dwarf will be cooling down and as a result, the amount of energy it emits will decrease



Lifecycle of Solar mass stars, downloadable IGCSE & GCSE Physics revision notes


The lifecycle of a solar mass star



Exam Tip

Make sure you remember the life cycle for a solar 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 solar mass star clearly (red giant, planetary nebula, white dwarf) as this is different for a star that is much larger than our Sun!