The Life Cycle of Solar Mass Stars (Edexcel GCSE Physics): Revision Note

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, thermal expansion from fusion reactions occur within its core 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 reactions in the star eventually die down as it runs out of fuel

• 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

• 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 as a planetary nebula

• 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

The lifecycle of a solar mass star