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 regions and pulled out a stream of gas and dust 100,000 light years long.[1] Its members are NGC 87, NGC 88, NGC 89 and NGC 92, discovered by John Herschel on the 30 September 1834.[2]

Robert's Quartet
Observation data (Epoch J2000)
Constellation(s)Phoenix
Right ascension0h 21m 23.075s
Declination−48° 37.75′ 39.5″
Brightest memberNGC 92
Number of galaxies4
Other designations
AM 0018-485

The quartet is one of the best examples of compact galaxy groups.[1] 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.[3] The quartet has a total visual magnitude of almost 13.[3] The brightest member of the group is NGC 92, having the blue magnitude of 13.8.[4] On the sky, the four galaxies are all within a circle of radius of 1.6 arcmin, corresponding to about 75,000 light-years.[3] It was named by Halton Arp and Barry F. Madore, who compiled A Catalogue of Southern Peculiar Galaxies and Associations in 1987.[3] Arp and Madore named Robert's Quartet after Robert Freedman who generated many of the updated positions of galaxies in the catalogue.[3]

Members
Members of Robert's Quartet
Name Type Distance from Sun
(million ly)		 Magnitude
NGC 87 IBm pec. ~160 +14.5
NGC 88 SB(rs)a pec. ~160 +15.21
NGC 89 SB0(s)a pec. ~160 +14.57
NGC 92 SAa pec. ~160 +14.29
The largest member of the galaxy group known as Roberts Quartet is NGC 92, a spiral Sa galaxy with an unusual appearance.

See also

References
  1. Darling, David. "Robert's Quartet". David Darling. Retrieved 21 January 2019.
  2. Herschel, John Frederick William (1847). Results of astronomical observations made during the years 1834, 5, 6, 7, 8, at the Cape of Good Hope: being the completion of a telescopic survey of the whole surface of the visible heavens, commenced in 1825. 1. London, United Kingdom: Smith, Elder and Co. p. 51.
  3. "Cosmic Portrait of a Perturbed Family". European Southern Observatory. Retrieved 21 January 2019.
  4. "NGC 92". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-09-24.


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