Galaxies are collections of stars, planets, gas, dust and dark matter held together by the force of gravity. The majority of galaxies contain a supermassive black hole at their centre.

Our galaxy is called the Milky Way. The closest galaxy to it is Andromeda. Other well-known galaxies include Messier 87 and Messier 101.

Galaxies can look quite different depending on what type they are and what they contain.

Spiral galaxies look like whirlpools of stars with a brighter spherical centre, and tend to be bluer.

Elliptical galaxies look like spheres of stars, and tend to be redder.

Galaxies can contain spiral arms, discs, bars, bulges, dust trails and rings.

SOURCE: Canadian Space Agency