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.
A diagram showing the life cycle of a star. A Protostar can become either a Black dwarf or Supernova. If it becomes a Supernova it can then develop into either a Black hole or a Neutron star.

All stars begin life in the same way.

A cloud of dust and gas, also known as a nebula, becomes a protostar, 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:

{protostar}\rightarrow{main~sequence~star}\rightarrow{red~giant~star}\rightarrow{white~dwarf}\rightarrow{black~ dwarf}

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.

Image of nebula, (cloud and dust in space that pull together to form a protostar)

Gravity begins to pull the dust and gas together.

Image of nebula, (cloud and dust in space that pull together to form a protostar) but some of the cloud and dust start to pull together, and a spherical outline can be seen.


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.

Image of a protostar, rocks and dust have been pulled together to form a strong outline of a sphere, though not a full sphere yet.

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.

Image of a main sequence star, a yellow sphere, wiith the occasional flare coming out. The core is a darker shade than the outer core, and the flares coming out a light still.

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.

Image of a red giant star. A red sphere in space, it is all one shade of red.

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.

Image of a white dwarf. A white sphere in space, and purposefully small in comparison to the overall image.