irregular galaxy

Irregular galaxy is a catch-all term for galaxies that do not fit the more defined shapes such as spiral galaxy or elliptical galaxy. Some sub-classifications:

• Irr-I - has hints of structure. (Some galaxies formerly classified as Irr-I with limited spiral structure are now given the "Sm" classification, which uses the Magellanic Clouds as its prototypes.)
• Irr-II - no such hints. The classification amorphous galaxy is a refinement of this classification.
• dIrr - dwarf irregular.

Irregular galaxies can have bars (i.e., a barred irregular galaxy). Some irregular galaxies are considered the results of galaxy mergers and tidal forces in other galaxy interactions.