What is an Irregular Galaxy?

An irregular galaxy is... irregular. With no definitive shape or structure, these galaxies are often chaotic in appearance and are thought to make up 20-25% of all galaxies in the universe. In many cases they are thought to have started out as spiral or elliptical galaxies but were then gravitationally disrupted by a galactic collision/near miss, or by being gravitationally influenced by a larger nearby galaxy. This type of galaxy is classified into three groups: Irr 1, an irregular galaxy with some structure, closely related to spiral galaxies in that they often have disks and bulges, but without any sort of spiral structure with a bulge located away from the center. Irr 2, a galaxy with a very little structure at all and dIrr, the smaller dwarf irregular galaxies.

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