Irregular Galaxy

                                                                As the name suggests, "irregular" galaxies have no specific form, and so the group contains a very diverse selection of objects. In fact, there are two types of irregular galaxy. Type I's are usually single galaxies of peculiar appearance. They contain a large fraction of young stars, and show the luminous nebulae that are also visible in spiral galaxies. Type II irregulars include the group known as interacting or disrupting galaxies, in which the strange appearance is due to two or more galaxies colliding, merging or otherwise interacting gravitationally. Type II's appear to contain a large amount of dust.

                                                               Most irregulars are small and faint. The dwarf irregulars may be the most common type of galaxy in the universe (or maybe the dwarf ellipticals are). The estimates of the number of dwarf irregulars and dwarf ellipticals are based on the proportions of these types of galaxies in nearby groups. The dwarf galaxies far away are too faint to be seen and are, therefore, overlooked in surveys of the sky. Perhaps if the dwarf galaxies were brighter, Hubble would have arranged the galaxies in a different sequence instead of the two-pronged sequence. Examples of irregular galaxies are the Large and Small Magellanic Clouds (two small irregulars that orbit the Milky Way). 

                                                               In the light of the name "irregular", it is perhaps surprising that some systematic structure is observed in the type I galaxies. In fact, they are most closely related to spirals, and this is a relation which is alluded to in the presence of disks and bulges like their more orderly counterparts. However, it is here that the similarity ends, since the disks of irregular galaxies certainly show no sign of the spiral structure, and the galactic bulges are not even located at the centre of the object .These galaxies may in some ways be regarded as "primitive". They are relatively poor in "heavy" elements