At odds with other galaxies, irregular galaxies do not have any recognizable
structure or symmetry. They are divided in two classes, Irr I (first type
irregulars) when their stars can be resolved, and Irr II (second type irregulars)
otherwise. Irregulars are often associated to a big spiral galaxy, they
are a kind of satellite. This is the case of the Small and Large Magellanic
Clouds, two small irregular galaxies, about 180,000 light years far from
the Milky Way. Irregular galaxies are just a small fraction of the total,
about 1%. They are rich in gas and dust, and are forming stars at a higher
rate than spirals. They contain many young stars, of the first spectral
types, that is massive-blue stars.
The "cigar shaped" galaxy M82, an Irr II galaxy in Ursa Major. This
galaxy has a companion, M81. (SEDS)
