Irregular galaxies get their odd shapes in many ways. One way irregular galaxies are formed is when galaxies collide or come close to one another, and their gravitational forces interact. Another source of irregular galaxies may be very young galaxies that have not yet reached a symmetrical state. Also, in some irregular galaxies, like M82, young stars eject energetic bubbles gas, giving the galaxy a blobby look. They are probably formed as galaxies collide or have companion galaxies that influence them.
Peculiar galaxies are generally smaller and optically dimmer than regular galaxies.
They have the designation p or pec at the end of their name. Arp suggested that peculiar galaxies create stars in intense bursts. The irregular shape may be the result of a disturbance, perhaps a collision of two galaxies. The irregular shape may be the result of a disturbance, perhaps a collision of two galaxies. It started out as a regular spiral galaxy that was hit by a smaller galaxy.