Irregular Galaxy

Irregular Galaxy - IRAS 19115-2124
Credit: ESO/VLT

An irregular galaxy does not have an obvious shape like spirals or ellipticals. They do not fall into any of the broad classes of the Hubble tuning fork.

Irregulars often look a mess. They show no trace of spiral structure or a central bulge. This can often be the result of a recent interaction with nearby galaxies.

These systems are also called peculiar. They make up around 25% of all known galaxies. In general these systems have lots of gas and dust in them. This means that they can be home to a lot of new stars being born.

The closest galaxy to the Milky Way is an irregular galaxy called the Canis Major Dwarf. It has only 1 billion stars. It is thought to be falling towards the Milky Way, and may one day become part of our spiral arms.