Galaxies are massive sprawling systems composed of stars, planets, gas clouds, dust, and dark matter that are all bound together by the force of gravity. They vary in size from small “dwarf” galaxies that may contain only a few thousand stars to giant galaxies that can hold up to a trillion stars or more.

Most large galaxies host a supermassive black hole at their centre. For example, our own Milky Way galaxy orbits around a central black hole called Sagittarius A*.

There could be between 100 billion to 2 trillion galaxies scattered across the observable universe.

They are not isolated; they group together into large, gravity-bound communities called galactic clusters.