Details: Stephen’s Quintet was discovered in 1877 by French astronomer, Édouard Jean-Marie Stephan, while serving as director of the Marseille Observatory where he spent considerable time improving the observatory with limited time for observations. Nevertheless, he discovered several NGC objects including these five galaxies now named after him.

Interestingly, only four of the five central galaxies in this image are part of the compact galaxy group. The bluish galaxy, NGC 7320, is much closer to us and, therefore, not a part of the merging group. Stephan’s Quintet is such an interesting and studied example of galactic mergers that it was selected as one of the early five astronomical objects observed by the new giant James Webb Space Telescope as seen here!

As early as the 1970s, radio telescopes detected a filament or bridge of material emitting light between several galaxies in the group. Both Hubble and Webb space telescopes as well as X-ray telescopes have provided insight into the filament showing it to be a shock wave of sorts, caused by collision of the galaxies’ intergalactic gasses. Particularly, the galaxy NGC 7318 is gravitationally falling into and colliding with the compact group of galaxies. The filament can be seen in the image above as a reddish and bluish arc connecting the arms of NGC 7318.

Redshift: As mentioned above, NGC 7320 is much closer to us than the other galaxies. This is known due to the redshift comparison between the five galaxies. Redshift is the increase in the wavelength of light emitted by an object. A redshift in light indicates the object moves away from us. A blueshift indicates it moves toward us. It is the same principle in which a train passing us decreases its pitch due to the increase of the wavelength of sound caused by the velocity of the receding train stretching the sound waves it produces. The redshift of NGC 7320 indicates it travels at only about 790 km/s away from us, while the redshift of the other four galaxies is around 6600 km/s, over 8 times faster! Using Hubble’s Law that states galaxies move away from us in proportion to their distance from us, we can estimate NGC 7320 is about 40 million light years away, making it a candidate for association with another galaxy group, NGC 7331, as are beautiful galaxies NGC 7320A and NGC 7320C also visible here. In contrast, the other four galaxies (NGC 7317, 7318A, 7318b, and 7319) are 8 times further away placing them somewhere between 210 and 340 million light years away!

Annotations. In the image above, hover a mouse or curser over the image to show annotations of the Stephen’s Quintet, with several enlarged insets identifying interesting features! Clicking on the image displays a full screen view of the galaxy group without animations that can be zoomed in further as desired. Starting on the far left are two enlarged insets of distant galaxies, an irregular spiral galaxy and spiral galaxy PGC 141039. At the bottom right is nearly edge on spiral galaxy NGC 7320A. Just to the right and below the center group of galaxies also is NGC 7320C. The other five galaxies in the center have insets labeled with their names NGC 7317, NGC 7318, NGC 7319, and NGC 7320.

Below Images: The image below is the same image as above but processed to remove all foreground stars. This is how the galaxies would appear if we were outside our own galaxy, since every star visible is within our own Milky Way Galaxy. Using a mouse to hover over the image brings all the stars back. Finally, the last image below is a zoomed in version of the compact galaxy group with and without stars!

Object Statistics: Constellation: Pegasus, Right Ascension: 22h 35m 57.5s, Declination: +33° 57' 36”, Apparent Magnitude: 13-14 each, Size: 2’ x 1’ each, Distance 200-340 million light-years.