Also found in: Dictionary.
stellar systems that are distinguished from spiral or elliptical galaxies by their lack of orderly structure and their patchy shape. Sometimes irregular galaxies that are amorphous and have no clear form are encountered. These consist of stars and dust, whereas the majority of irregular galaxies also contain gas and a large number of very bright, hot blue giants. Clusters of the latter create the appearance of patchiness. There are irregular galaxies that have traces of spiral structure, in particular, the stellar systems closest to our galaxy, the Magellanic Clouds. Only a small number of galaxies are irregular.