NGC 7331 – The Deer Lick Group and Stephan's Quintet
Key Scientific Data
Object type: Unbarred spiral galaxy – SA(s)b
Constellation: Pegasus
Other designations: Caldwell 30, UGC 12113, PGC 69327
Distance from Earth: approximately 45–50 million light-years
Diameter: approximately 120,000 light-years
Apparent size: approximately 10.5′ × 3.7′
Apparent magnitude: approximately 9.5–10.4, depending on the photometric band
Inclination: approximately 75–77°
Right Ascension: 22h 37m 04s
Declination: +34° 25′
Discovered by: William Herschel, 1784
Nucleus: Hosts a supermassive black hole
Light-travel time: approximately 45–50 million years
Description
NGC 7331 is a large spiral galaxy approximately 45–50 million light-years away, comparable in size to the Milky Way.
Its highly inclined disc reveals a prominent central bulge, intricate dust lanes and spiral arms containing young stellar populations. The warmer yellowish nucleus contrasts with the bluish outer regions, while small reddish areas trace ionised hydrogen associated with ongoing star formation.
The high-resolution view obtained with the Artesky ARTEC 250 Pro reveals the galaxy's complex internal structure and dust distribution.
A Twin of the Milky Way?
NGC 7331 is sometimes considered a twin of the Milky Way because of its similar size and overall spiral structure.
However, unlike our barred spiral galaxy, NGC 7331 is classified as an unbarred spiral, offering an external perspective on a broadly comparable galactic system.
Curiosities
Discovered by William Herschel in 1784, NGC 7331 exhibits an unusual feature: spectroscopic studies have identified a counter-rotating stellar component within its central region, possibly linked to past interactions or accretion events.
Its apparent association with several nearby-looking galaxies also provides a remarkable example of perspective effects in astronomy.
The Deer Lick Group
NGC 7331 appears alongside NGC 7335, NGC 7336, NGC 7337 and NGC 7340, forming the apparent grouping known as the Deer Lick Group.
Despite their proximity in the sky, these smaller galaxies lie hundreds of millions of light-years farther away. The group is therefore an optical alignment rather than a single gravitationally bound system.
A Deeper Extragalactic Field
Numerous faint background galaxies are scattered across the image, some appearing as tiny elongated or diffuse structures.
The field also extends towards Stephan's Quintet, a famous compact galaxy group. Four of its principal members lie approximately 280–300 million light-years away, while NGC 7320 is a much closer foreground galaxy.
Together, these systems reveal the remarkable range of cosmic distances contained within a single astronomical field.
Looking Back in Time
The light captured from NGC 7331 began its journey approximately 45–50 million years ago, during Earth's Eocene epoch.
At that time, Earth was considerably warmer than today, tropical forests extended into higher latitudes, and early mammals, including ancestors of horses, whales and primates, were evolving. Humans had not yet appeared, and the earliest hominins were still tens of millions of years away.
The more distant members of Stephan's Quintet reveal an even earlier period, approximately 280–300 million years ago, during the late Carboniferous to early Permian. Vast forests, giant insects and early reptiles inhabited Earth, while the supercontinent Pangaea was forming. Dinosaurs would not appear for another 50 million years or more.
This photograph captures galaxies whose light began travelling towards Earth during profoundly different chapters of our planet's history.
Image Data
Total integration time: 21h 55m
Integration by filter:
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Luminance/Clear: 5h (60 × 300")
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Red: 6h 29m 45s
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Green: 5h 45m 30s
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Blue: 4h 39m 45s
Equipment:
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Telescope: Artesky ARTEC 250 Pro
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Camera: Player One Poseidon-M Pro
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Mount: 10Micron GM2000 HPS II
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Filters: Antlia V-Pro LRGB 2"
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Accessories: Pegasus Astro Prodigy Microfocuser, Player One Phoenix Wheel 7×2", WandererAstro WandererCover V4-EC
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Software: Adobe Photoshop, Pleiades Astrophoto PixInsight, Stefan Berg Nighttime Imaging 'N' Astronomy (N.I.N.A. / NINA)
For further information and the full-resolution image, visit AstroBin: