Robert's Quartet is a compact

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 galaxies ...

approximately 160 million

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s away 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 ...

Phoenix Phoenix most often refers to: * Phoenix (mythology), a legendary bird from ancient Greek folklore * Phoenix, Arizona, a city in the United States Phoenix may also refer to: Mythology Greek mythological figures * Phoenix (son of Amyntor), a ...

. It is a family of four very different

galaxies 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. ...

whose proximity to each other has caused the creation of about 200 star-forming regions and pulled out a stream of gas and dust 100,000 light years long. Its members are

NGC 87 NGC 87 is a diffuse, highly disorganized barred irregular galaxy, part of Robert's Quartet, a group of four interacting galaxies. See also * Robert's Quartet References External links NGC 87http://www.astro.pef.zcu.cz/ * {{DEFAULTSORT: ...

NGC 88 NGC 88 is a barred spiral galaxy exhibiting an inner ring structure located about 160 million light years from the Earth in the Phoenix constellation. NGC 88 is interacting with the galaxies NGC 92, NGC 87 and NGC 89. It is part of a family o ...

NGC 89 NGC 89 is a barred spiral or lenticular galaxy, part of Robert's Quartet, a group of four interacting galaxies. This member has a Seyfert 2 nucleus with extra-planar features emitting H-alpha radiation. There are filamentary features on each ...

and

NGC 92 NGC 92 is a highly warped interacting unbarred spiral galaxy in Robert's Quartet; it is interacting with three neighbouring galaxies NGC 87, NGC 88 NGC 88 is a barred spiral galaxy exhibiting an inner ring structure located about 160 million ...

, discovered by

John Herschel Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint and did botanical wor ...

on the 30 September 1834. The quartet is one of the best examples of compact galaxy groups. Because such groups contain four to eight galaxies in a very small region they are excellent laboratories for the study of galactic interactions and their effects, in particular on the formation of stars. The quartet has a total visual magnitude of almost 13. The brightest member of the group is NGC 92, having the blue magnitude of 13.8. On the sky, the four galaxies are all within a circle of radius of 1.6 arcmin, corresponding to about 75,000 light-years. It was named by

Halton Arp Halton Christian "Chip" Arp (March 21, 1927 – December 28, 2013) was an American astronomer. He was known for his 1966 ''Atlas of Peculiar Galaxies'', which (it was later theorized) catalogues many examples of interacting and merging galaxie ...

and Barry F. Madore, who compiled ''A Catalogue of Southern Peculiar Galaxies and Associations'' in 1987. Arp and Madore named Robert's Quartet after Robert Freedman who generated many of the updated positions of galaxies in the catalogue.

Members

References

External links

ESo: Cosmic Portrait of a Perturbed Family

* Phoenix (constellation) Galaxy clusters {{galaxy-cluster-stub