A peculiar galaxy is a

galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...

of unusual size, shape, or composition. Between five and ten percent of known galaxies are categorized as peculiar. Astronomers have identified two types of peculiar galaxies: ''interacting galaxies'' and ''active galactic nuclei'' (AGN). When two galaxies come close to each other, their mutual

gravitational In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong ...

forces can cause them to acquire highly irregular shapes. The terms 'peculiar galaxy' and 'interacting galaxy' have now become synonymous because the majority of peculiar galaxies attribute their forms to such gravitational forces.

Formation

Scientists hypothesize that many peculiar galaxies are formed by the collision of two or more galaxies. As such, peculiar galaxies tend to host more active galactic nuclei than normal galaxies, indicating that they contain

supermassive black holes A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical ob ...

. Many peculiar galaxies experience starbursts, or episodes of rapid star formation, due to the galaxies merging. The periods of elevated star formation and the

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

resulting from active

galactic nuclei An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not pr ...

cause peculiar galaxies to be slightly bluer in color than other galaxies. Studying peculiar galaxies can offer insights on other types of galaxies by providing useful information on galactic formation and evolution. Arp mapped peculiar galaxies in his 1966

Atlas of Peculiar Galaxies The ''Atlas of Peculiar Galaxies'' is a catalog of peculiar galaxies produced by Halton Arp in 1966. A total of 338 galaxies are presented in the atlas, which was originally published in 1966 by the California Institute of Technology. The ...

. Arp states that "the peculiarities of the galaxies pictured in this Atlas represent perturbations, deformations, and interactions which should enable us to analyze the nature of the real galaxies which we observe and which are too remote to experiment on directly."

Notation

Peculiar galaxies are notated by an additional "p" or "pec" (depending on the exact convention) after the Hubble type of the galaxy.

External links

{{DEFAULTSORT:Peculiar Galaxy Galaxy morphological types

Formation

Notation

See also

External links