Introductory Astronomy: Irregular Galaxies

Irregular galaxies are just that: irregular. They do not fit into the spiral/elliptical classification scheme Hubble developed, nor do they show distinctive features as a class. They are generally just a conglomeration of galaxies which are united only by the fact that they don't belong anywhere else.

Irregular galaxies have a chaotic appearance, with large clouds of gas and dust mixed with both old and young stars at random. They have no apparent spiral arms or nuclear bulge. Irregulars are generally faint. They make up probably about 25% of all galaxies.

Irregular galaxies are divided into two groups. Type Irr I galaxies can be resolved into nebulae, stars. and clusters; type Irr II galaxies cannot be resolved into these components. Other than this classification, irregular galaxies can have pretty much any shape they please.

The best-studied examples of irregular galaxies are the Large and Small Magellanic clouds (LMC and SMC ), which are members of our own cluster of galaxies, called the Local Group.