M51 – The Whirlpool Galaxy
Key Scientific Data
Object type: Grand-design spiral galaxy – SA(s)bc
Constellation: Canes Venatici
Other designations: NGC 5194, UGC 8493, PGC 47404, Whirlpool Galaxy
Companion galaxy: NGC 5195
Distance from Earth: approximately 31 million light-years
Diameter: approximately 85,000–90,000 light-years
Apparent size: approximately 11′ × 7′, including its companion
Apparent magnitude: approximately 8.4
Orientation: Nearly face-on
Right Ascension: 13h 29m 53s
Declination: +47° 12′
Discovered by: Charles Messier, 1773
Spiral structure first recognised by: Lord Rosse, 1845
Nucleus: Active galactic nucleus containing a supermassive black hole
Light-travel time: approximately 31 million years
Description
Messier 51 (M51), the Whirlpool Galaxy, is a grand-design spiral galaxy approximately 31 million light-years away, renowned for its exceptionally well-defined spiral structure.
Its nearly face-on orientation reveals two prominent spiral arms extending from a bright central region. Bluish stellar populations and reddish hydrogen-emission regions trace ongoing star formation, while dark dust lanes outline the spiral pattern.
At its centre lies an active galactic nucleus containing a supermassive black hole.
A Grand-Design Spiral
M51 is one of the finest examples of a grand-design spiral galaxy, characterised by two continuous, symmetrical spiral arms.
Its distinctive morphology has been strongly influenced by gravitational interactions with its smaller companion, NGC 5195. These interactions have enhanced the spiral structure and stimulated star formation by compressing interstellar gas.
Two Galaxies in a Gravitational Dance
NGC 5195, the smaller yellowish companion, is physically interacting with M51 rather than merely appearing nearby.
Their gravitational encounters have distorted both galaxies, producing tidal structures, diffuse stellar streams and a bridge of material connecting the two systems.
NGC 5195 is dominated by older stellar populations and also hosts a supermassive black hole. Observations have revealed energetic nuclear activity and extended structures of hot gas, potentially associated with past interactions.
A Field Shaped by Gravity
The deep integration reveals extremely faint tidal material extending beyond the bright galactic discs, particularly around NGC 5195.
These diffuse structures preserve evidence of gravitational encounters and the redistribution of stars and gas between the galaxies.
The field also contains several distant background galaxies, including IC 4263, visible as a narrow, nearly edge-on system towards the lower-left area of the photograph, and IC 4277 and IC 4278 near the interacting pair.
Foreground Milky Way stars complete a field containing objects at widely different distances.
Curiosities
M51 was discovered by Charles Messier in 1773, while its companion NGC 5195 was subsequently identified by Pierre Méchain.
In 1845, William Parsons, Third Earl of Rosse, observed M51 with his 72-inch Leviathan of Parsonstown, becoming the first astronomer to clearly recognise a spiral structure in a celestial object.
At the time, M51 was still considered a spiral nebula within the Milky Way. Its true nature as an independent galaxy would only be established during the twentieth century.
Looking Back in Time
The light captured from M51 and NGC 5195 began its journey approximately 31 million years ago, during Earth's early Oligocene epoch.
At that time, the planet was undergoing significant climatic cooling following the warm Eocene. Antarctic ice sheets were expanding, forests were retreating in some regions, and mammals were diversifying into increasingly recognisable groups, including early ancestors of modern horses, elephants and primates.
Humans had not yet appeared, and the earliest hominins would not emerge for another 20 million years or more. Modern humans, agriculture and the first civilisations were still far in the future.
Throughout these profound changes in Earth's environment and evolution, the photons recorded in this image travelled across intergalactic space.
This photograph captures two interacting galaxies as they appeared 31 million years ago, preserving an ancient chapter of their gravitational evolution.
Image Data
Total integration time: 23h 45m
Integration by filter:
-
L-Pro: 5h 40m (68 × 300")
-
Red: 5h 51m 40s
-
Green: 5h 22m 40s
-
Blue: 6h 50m 40s
Equipment:
-
Telescope: Artesky ARTEC 250 Pro
-
Camera: ToupTek ATR2600M
-
Mount: 10Micron GM2000 HPS II
-
Filters: Optolong L-Pro, Red, Green, Blue 2"
-
Accessories: Pegasus Astro Prodigy Microfocuser, ToupTek AFW-L 7×2", WandererAstro WandererBox Pro V3
-
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: