NGC 1427A, an example of an irregular galaxy about 52 million light years distant.

Tuning-fork style diagram of the Hubble sequence

An irregular galaxy is a galaxy that does not have a distinct regular shape, like a spiral or an elliptical galaxy.

Irregular galaxies do not fall into any of the regular types of the Hubble sequence. They do not have a bulge in the centre, nor any trace of spiral structure. They are quite common: they may make up a quarter of all galaxies. Most were once spiral or elliptical galaxies but were deformed by gravitational pull. Irregular galaxies also contain abundant amounts of gas and dust.