What is Galaxy

A galaxy is a vast collection of stars,  dust, and gases held together by the gravitational attraction between it's components.

Most of the galaxyies are either spiral or elliptical. Elliptical galaxies are very bright while spiral galaxies are usually much bigger.

Elliptical galaxies are made of old stars. They are the most massive galaxies containing trillions of stars. Irregular galaxies have no apparent structure or shape.