The Formation of the Sun (AQA GCSE Physics)

• The Sun is formed from massive clouds of dust and gas in space
  • A cloud of dust and gas in space is called a nebula

A nebula is a cloud of gas and dust in space (Image courtesy of NASA)

• Gravity pulled this cloud together into a giant ball

The nebula collapses due to gravity and begins to rotate (Image courtesy of NASA)

• As the nebula collapsed the centre of this ball got very dense and hot and began to rotate
• Eventually nuclear fusion  was able to begin and a dense protostar was formed – our Sun

Our Sun (Image courtesy of NASA)

• 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 of pressure
  • This is an outward force which is exerted from the expanding hot gases inside the star

Equilibrium in Stars

• When the inward pull of gravity and the outward pressure acting on the star are equal the star will be in equilibrium

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 (because, perhaps, the rate of fusion has slowed) the outward pressure will also decrease
  • This will cause the star to contract