A peculiar galaxy is a galaxy of unusual size, shape, or composition.[1] Between five and ten percent of known galaxies are categorized as peculiar.[2] Astronomers have identified two types of peculiar galaxies: interacting galaxies and active galactic nuclei (AGN).[3]
When two galaxies come close to each other, their mutual gravitational forces can cause them to acquire highly irregular shapes.[4] The terms 'peculiar galaxy' and 'interacting galaxy' have now become synonymous because the majority of peculiar galaxies attribute their forms to such gravitational forces.[2]