Equilibrium in Stars (Edexcel GCSE Physics)

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Equilibrium in Stars

  • Stars are held together by a delicate balance of inwards and outwards forces
  • One of these forces is the force of gravity
    • This is an attractive force which pulls the outer layers inwards

  • The other force is the force from the pressure caused by the thermal expansion
    • This is an outward force which is exerted from the expanding hot gases inside the star

  • When the inward pull of gravity and the force from the outward thermal expansion acting on the star are equal, the star will be in equilibrium
  • This is how the stars in the main sequence remain stable for millions of years

hydrostatic-equilibrium, IGCSE & GCSE Physics revision notes

Forces acting within a star. The centre red circle represents the star’s core and the orange circle represents the stars outer layers

  • If the temperature of a star increases, the outward pressure will also increase
    • This will cause the star to expand

  • If the temperature drops the outward pressure will also decrease
    • This will cause the star to contract

  • As long as these two forces balance, the star will remain stable
  • Once these forces are unbalanced, then they will no longer be in equilibrium causing the star to expand or contract
    • This happens when fusion in the core of stars, and hence thermal expansion, ceases at the end of the star's life

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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.