Photo Credit: NASA/JPL Spitzer Space Telescope: CLICK for larger image and see below for information and links.

If our eyes could see in infrared (24 micrometers or microns) and you looked to the night sky, this is close to how you would view our closest non-dwarf neighbor. In this 11,000 photo mosaic, Spitzer shows us Andromeda and her spiral lanes in incredible detail. It’s been known that something was a little “off” with Andromeda in regard to the spiral structures asymmetrical stature and stability. It’s been discovered that the ring structure is split into two pieces and it could be from interactions with satellite galaxy, namely M32 as it’s believed to have passed through the plane of the galaxy approximately 210 million years ago.

M31 or as it’s known, the Andromeda Galaxy is a relatively close spiral galaxy 2.5 million light years away and closing in on the Milky Way at 190 miles (300 km) per second with a predicted collision scheduled in about 3.8 to 4.5 billion years from now as the two galaxies rush along through the cosmos. In the collision the Milky Way’s approximate 200-400 billion stars will merge with Andromeda’s trillion stars to form a massive elliptical galaxy. A strange fact that lends itself as a demonstration to the massive distances in space is that during the collision it’s predicted that no two stars will collide during the event. M31 is the most distant naked eye object readily visible and we view it at an angle of 77 degrees relative to Earth, where if it were 90 we would see it face on.
In our “Local Group” of approximately 54 galaxies, M31 and the Milky Way are the two largest with M31 at approximately 200,000 light years in diameter is roughly double the size with an approximate mass equal to the mass of our home city due to the Milky Way containing much more Dark Matter. M31 is also home to approximately 19 satellite galaxies (14 being dwarf galaxies) and 460 globular clusters. The “Local Group” is a relatively small collection of calaxies within the Virgo Supercluster of galaxies.
In addition to all this, twenty six stellar-mass black hole candidates have been discovered in Andromeda as well; eight of which are associated with globular clusters. This, of course, is in addition to the relatively quiet supermassive black hole at its core.
The formation of M31 is believed to have been pretty chaotic as it’s theorized that it is the end result of the merger of two smaller galaxies between 5 and 9 billion years ago. About 3 or 4 billion years ago Andromeda and the Triangulum Galaxy (M33) had a close encounter which produced high levels of stellar formation through the disk. This also created a disturbance in the disk of M33.
A note on motion: Galactic motion is pretty complex but it goes something like this. Our Local Group of roughly 54 galaxies is falling inward, deeper toward the Virgo Supercluster (In Virgo) at about 1 million mph which is, itself moving toward the Great Attractor (In Hydra & Centaurus) 250 million light years away at 14 million mph (22 million km/h). It’s truly much more complex than that as within the clusters and local groups, due to individual galaxies interactions with each other, the galaxies themselves can (and do) move in individual directions as they eventually careen towards the center.

NAME: Andromeda, Messier 31, M31, NGC 224.

WHAT IS IT?: Spiral Galaxy and our closest non-dwarf neighbor as well as the largest galaxy in our local group in size.

HOW FAR AWAY IS IT?: Currently 2.5 million light years distant.

HOW BIG IS IT?: Approximately 200,000 light years in diameter (twice that of the Milky Way) with a mass roughly equal to it. On the night sky it is 190’ x 60’ arcminutes or about 4 degrees which equates to 6 times the diameter of the average full moon.

APPARENT MAGNITUDE?: 3.44 or +3.44 which is naked eye visible from dark locations.

WHERE IS IT? (General): Constellation Andromeda.

WHERE IS IT? (Exact RA/DEC J2000): RA 00h 42m 44.3s / DEC +41° 16′ 9″.

Spitzer page for this image:

NASA APOD for this image:

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