Stellar evolution

The evolution of a star can be shown on the HR diagram.

Key Concepts

This diagram (by R.N. Bailey) shows a summary of the stages in the evolution of a star's life that we have covered so far.

Star Life Cycle Chart

Note the importance of the mass of the star in determining:

  • Whether a protostar commences fusion to join the main sequence or becomes a brown dwarf
  • The stellar classification of the star during the main sequence
  • Whether a supernova results in the formation of a neutron star or black hole


The changes between the main sequence, giant / super giant and white dwarf stages can be represented on the HR diagram.

Stellar evolution L vs T

Taking these in turn:

  1. Shows a star's entry to the main sequence, as its protostar rises in temperature and commences fusion.
  2. Shows a star's move from the main sequence to the giant stage, with a reduction in temperature due to the increase in radius and an increase in luminosity associated with helium fusion.
  3. Shows the end of the red giant stage with the shedding of the planetary nebula as the star expands for the last time.
  4. Shows the cooling of a white dwarf corresponding with its decline in luminosity due to the absence of fusion.


Test Yourself

Use flashcards to practise your recall.

Use quizzes to practise application of theory.