The life cycle of stars - Higher
The life cycle for a particular star depends on its size. The diagram shows the life cycles of stars that are:
- about the same size as the Sun;
- far greater than the Sun in size.
All stars begin life in the same way.
A cloud of dust and gas, also known as a nebula, becomes a The early stage in the formation of a star, before nuclear fusion occurs. which goes on to become a main sequence star.
Following this, stars develop in different ways depending on their size.
Stars that are a similar size to the Sun follow the left hand path shown in the diagram above:
\(\begin{equation} \begin{aligned} {protostar} \rightarrow {main~sequence~star} \rightarrow {red~giant~star} \rightarrow \\ {white~dwarf} \rightarrow {black~ dwarf} \end{aligned} \end{equation}\)
A nebula
A star forms from massive clouds of dust and gas in space, also known as a nebula. Nebulae are mostly composed of hydrogen.
Gravity begins to pull the dust and gas together.
Protostar
As the mass falls together it gets hot. A star is formed when it is hot enough for the hydrogen nuclei to fuse together to make helium. The fusion process releases energy, which keeps the core of the star hot.
Main sequence star
During this stable phase in the life of a star, the force of gravity holding the star together is balanced by higher pressure due to the high temperatures. The Sun is at this stable phase in its life.
Red giant star
When all the hydrogen has been used up in the fusion process, larger nuclei begin to form and the star may expand to become a red giant.
White dwarf
When all the nuclear reactions are over, a small star like the Sun may begin to contract under the pull of gravity. In this instance, the star becomes a white dwarf which fades and changes colour as it cools.