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Friday, September 17, 2021

09-17-2021-0156 - Robert's Quartet

 Robert's Quartet is a compact galaxy group approximately 160 million light-yearsaway 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]

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]

Robert's Quartet
Phot-34a-05-fullres.jpg
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 largest member of the galaxy group known as Roberts Quartet is NGC 92, a spiral Sa galaxy with an unusual appearance.

https://en.wikipedia.org/wiki/Robert%27s_Quartet

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