Posted on Aug 27, 2020

APOD: 2020 August 27 - Shell Galaxies in Pisces

Maj William W. 'Bill' Price

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Good morning, Rallypoint. Today's Astronomy Picture of the Day (APOD) is titled "Shell Galaxies in Pisces." A shell galaxy is a type of elliptical galaxy where the stars in the galaxy's halo are arranged in concentric shells. The shell-like structures are thought to develop when a larger galaxy absorbs a smaller companion galaxy. As the two galaxy centers approach, the centers start to oscillate around a center point, the oscillation creates gravitational ripples forming the shells of stars, similar to ripples spreading on water.

We can see examples of a shell galaxies in today's APOD. Lying some 100 million light years distant in the constellation Pisces, spiral-armed NGC 470 appears adjacent to shell galaxy NGC 474 (left to right, respectively). Shell structures have never been observed in galactic spirals. The large galaxy on the top lefthand side of the deep image, NGC 467, appears to be surrounded by faint shells too, evidence of another interacting galaxy system.

APOD: 2020 August 27 - Shell Galaxies in Pisces

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LTC Stephen F.

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Laura Veirs - Galaxies (Video)

2006 WMG Galaxies (Video)

Thank you my friend Maj William W. 'Bill' Price for posting the NASA Astronomy Picture of the Day (APOD) for Thursday, August 27, 2020 entitled "Shell Galaxies in Pisces."
Image: Shell Galaxies in Pisces - Image Credit & Copyright - Martin Pugh

APOD background
"Explanation: This intergalactic skyscape features a peculiar system of galaxies cataloged as Arp 227 some 100 million light-years distant. Swimming within the boundaries of the constellation Pisces, Arp 227 consists of the two galaxies prominent right of center, the curious shell galaxy NGC 474 and its blue, spiral-armed neighbor NGC 470. The faint, wide arcs or shells of NGC 474 could have been formed by a gravitational encounter with neighbor NGC 470. Alternately the shells could be caused by a merger with a smaller galaxy producing an effect analogous to ripples across the surface of a pond. The large galaxy on the top lefthand side of the deep image, NGC 467, appears to be surrounded by faint shells too, evidence of another interacting galaxy system. Intriguing background galaxies are scattered around the field that also includes spiky foreground stars. Of course, those stars lie well within our own Milky Way Galaxy. The field of view spans 25 arc minutes or about 1/2 degree on the sky."

Laura Veirs - Galaxies (Video)
https://www.youtube.com/watch?v=PE1ges9nn6A

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LTC Stephen F.

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