A peculiar galaxy is a
galaxy which is unusual in its size, shape, or composition. Peculiar galaxies
come about as a result of interactions between galaxies, and they may contain
atypical amounts of dust or gas, may have higher or lower surface brightness
than a typical galaxy, or may have features such as nuclear jets. They can be
highly irregular in shape due to the immense gravitational forces which act on
them during encounters with other galaxies.