The Formation of the Sun (AQA GCSE Physics)

The Formation of the Sun

• 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)

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 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