Stephan's Quintet, (HCG 92, Arp 319), NGC 7320 Galaxy Group, Pegasus, 30% CROP

Stephan's Quintet, (HCG 92, Arp 319), NGC 7320 Galaxy Group, Pegasus

This tight visual grouping of five galaxies was discovered in 1877 by Edouard Stephan at the Marseilles Observatory with the revolutionary 80 cm Foucault reflector, which was among the first to use a mirror of silvered glass, instead of speculum metal. The Quintet is the first compact group of galaxies ever documented. It has been carefully studied by numerous observatories ever since because it shows three galaxies in the process of merging, NGC7318-A, NGC7318-B, and NGC7319. All three appear to be barred spiral galaxies, severely distorted by tidal interactions. All display elongated and disrupted spiral arms, faint tidal tails of stars and gas drawn out from the galaxies into intergalactic space, and numerous bright blue regions of countless new stars ignited by gravitational perturbations of hydrogen clouds. Hubble's multi-band images in visible and infrared light reveal stellar populations of several age groups, indicating that starburst activity occurred in different epochs over hundreds of millions of years. In the long run, after billions of years, the three galaxies are destined to merge into a single giant elliptical galaxy. Based on their redshifts, and assuming Hubble Flow, the three galaxies lie at light travel distances between 267 and 312 million light years. However, they are probably much closer together. Due to strong gravitational interaction, they must have high peculiar velocities through space, which renders their distance estimates based on Hubble Flow unreliable.
www.cloudynights.com/articles/cat/articles/basic-extragal...

The fourth galaxy in the group is a modest elliptical galaxy, NGC 7317, gravitationally bound to its companions, but so far morphologically unaffected. These four galaxies are also gravitationally bound to the distant members of the Deer Lick Group, from which they are separated by only 35 arcmin.
www.cloudynights.com/topic/802766-ngc-7331-deer-lick-gala...

The most prominent galaxy in Stephan's Quintet is NGC 7320, a bright dwarf unbarred spiral which is actually 8 times closer than the other members of the visual grouping, and is gravitationally unbound to them. Based on its measurable properties (redshift, apparent magnitude, and angular size), it lies at a light travel distance of 36.4 Mly, receding at 706 km/s due to Hubble Flow (the expansion of space). Its diameter is only about 25,000 ly, five times smaller than the Milky Way's, and absolute magnitude some twenty times fainter. Blue color indicates a high star formation rate and a profusion of large, young, and very hot stars.

The most distant galaxy in the field is 2MFGC 17021, a large edge-on spiral, approximately the same size as the Milky Way, but about twice as bright. It is 784 Mly distant, receding at 17,113 km/s.

Image Details:
-Remote Takahashi TOA 150 x 1105 mm
-Paramount GT GEM
-25 x 300 sec subs, OSC, 2x drizzle, 30% linear crop
-Software: DSS, XnView, StarTools v 1.3 and 1.7, Cosmological Calculator v 2

Taken on: January 18, 2022

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