Life Cycle and Formation of Stars

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The following contains all you need to know about the life cycle of stars and their formation for GCSE Physics under Edexcel's specifications.

1. Stars start as clouds of dust and gas called nebulas
2. The force of gravity causes the dust and gas to spiral together as gravitational energy is converted to heat energy, causing a temperature increase
3. When the temperature increases high enough, hydrogen nuclei undergo thermonuclear fusion to form helium nuclei, which gives out massive amounts of energy – and so a star is created. It enters a long stable period where the heat generated by fusion provides an outward pressure to balance the force of gravity – everything is pulled inwards – lasting several billion years. This is called a main sequence star
4. The hydrogen in the core eventually begins to run out and the star will swell, turning into a red giant

 If it is a small star:

•  A small-to-medium sized star, like our Sun, will become unstable and eject its outer layer of dust and gas as a planetary nebula
• This process leaves a hot, dense solid core known as a white dwarf, which cools down and eventually disappears

If it is a large star:

• It will glow brightly again as it undergoes more fusion reactions and also expand and contract several times, forming heavier elements during nuclear reactions – it will explode as a supernova
• Next, it may become a neutron star when the supernova ejects its outer layers of dust and gas into space, to leave just a dense core
• Or, if the star is big enough, it will become a black hole