What cosmic accident is believed to form many irregularly shaped galaxies?

The kind of cosmic accident which is believed to form many irregular shaped galaxies is known as Galactic Collisions. Galactic Collisions are cosmic accidents that create irregularly shaped galaxies. The Andromeda-Milky Way Collision is one example of galactic collision that is predicted to occur in the next four (4) billion years, where the Andromeda and the Milky Way galaxy collide will collide with each other to form a new galaxy.