NGC 7331 Group is a visual grouping of galaxies in the
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the e ...
Pegasus
Pegasus ( grc-gre, Πήγασος, Pḗgasos; la, Pegasus, Pegasos) is one of the best known creatures in Greek mythology. He is a winged divine stallion usually depicted as pure white in color. He was sired by Poseidon, in his role as hor ...
.
Spiral galaxy
Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''NGC 7331 is a foreground galaxy in the same field as the collection, which is also called the ''Deer Lick Group''. It contains four other members, affectionately referred to as the "fleas": the lenticular or unbarred spirals NGC 7335 and NGC 7336, the
barred spiral galaxy
A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies, and generally affect both the motions of stars and interstellar gas within spiral galaxi ...
elliptical galaxy
An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The R ...
NGC 7340. These galaxies lie at distances of approximately 332, 365, 348 and 294 million light years, respectively. Although adjacent on the sky, this collection is not a
galaxy group
A galaxy group or group of galaxies (GrG) is an aggregation of galaxies comprising about 50 or fewer gravitationally bound members, each at least as luminous as the Milky Way (about 1010 times the luminosity of the Sun); collections of galaxie ...
, as NGC 7331 itself is not gravitationally associated with the far more distant "fleas"; indeed, even they are separated by far more than the normal distances (~2 Mly) of a galaxy group.
See also
* Stephan's Quintet, another visual grouping that is not (purely) a galaxy group. Ironically, its non-group member, NGC 7320, might be a member of a true NGC 7331 group, having a similar redshift to that nearby galaxy.
* Wild's Triplet
* Zwicky's Triplet
*
Robert's Quartet
Robert's Quartet is a compact galaxy group approximately 160 million light-years away in the constellation Phoenix. It is a family of four very different galaxies whose proximity to each other has caused the creation of about 200 star-forming ...
*
Seyfert's Sextet
Seyfert's Sextet is a group of galaxies about 190 million light-years away in the constellation Serpens. The group appears to contain six members, but one of the galaxies, NGC 6027d, is a background object and another "galaxy," NGC 6027e, is ...
, another visual grouping that is not (purely) a galaxy group, as one galaxy is a gravitationally unbound background object and another galaxy a tidal tail of stars.
*
Copeland Septet
The Copeland Septet (also Copeland's Septet, Hickson Compact Group 57) is a group of galaxies in the constellation Leo that includes NGC 3748, NGC 3754, NGC 3750, NGC 3751, NGC 3745, NGC 3753 and NGC 3746. The group was discovered by Brit ...