Andromeda's satellite galaxies

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The Andromeda Galaxy has satellite galaxies just like the Milky Way Galaxy. Orbiting Andromeda (M31) are at least 14 dwarf galaxies. The brightest and largest of them all is M32 which can be seen with a backyard telescope. The second & closest one is M110. The other galaxies are not as easy to see. They were found very recently and were hard to find in the first place.

It was announced on January 11, 2006 that astronomers have discovered that Andromeda's faint companion galaxies lie within a thin sheet running through Andromeda's center. This unexpected distribution is not obviously understood in the context of current models for galaxy formation. The plane of satellite galaxies points toward a nearby group of galaxies (M81 group), possibly tracing the large-scale distribution of dark matter.

[edit] Table of known satellites

Andromeda's satellites are listed here by discovery (orbital distance is not known). Satellites that can be seen through a telescope are highlighted in purple.

**Andromeda's satellites**
Name	Type	Distance from Sun (million ly)	Magnitude	Year discovered
M32	dE2	2.48	+9.2	1749
M110	dE6	2.69	+9.4	1773
NGC 185	dE5	2.01	+11	1787
NGC 147	dE5	2.2	+12	1829
Andromeda I	dSph	2.43	+13.2	1970
Andromeda II	dSph	2.13	+13	1970
Andromeda III	dSph	2.44	+10.3	1970
Andromeda IV ^*	dIm?			1972
Andromeda V	dSph	2.52	+15.4	1998
Pegasus Dwarf (Andromeda VI)	dSph	2.55	+14.5	1998
Cassiopeia Dwarf (Andromeda VII)	dSph	2.49		1998
Andromeda VIII	dSph	2.7	+9.1	2003
Andromeda IX	dSph	2.5	+16.2	2004
Andromeda X	dSph	2.9	+16.2	2005
Triangulum Galaxy (M33)	SA(s)cd	2.59	+6.27	1654?

^* It is uncertain whether is a companion galaxy of the Andromeda Galaxy.

[edit] Interacting with Andromeda

Andromeda Galaxy (M31) in Infrared, with the hole arc at bottom right

New images from NASA's Spitzer Space Telescope shed light on the Andromeda Galaxy's violent past. The images show that one of Andromeda's satellite galaxies, M32, blasted through one of Andromeda's spiral arms a few million years ago. Astronomers made an infrared picture of Andromeda's two spiral arms and prominent star-forming ring are separate structures. The images also show a hole where the rings seem to split into arcs. This hole is where astronomers believe M32 punched through Andromeda's galactic disk.