List of Andromeda's satellite galaxies

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The Andromeda Galaxy with M110 at upper left and M32 to the right of the core.

The Andromeda Galaxy (M31) has satellite galaxies just like the Milky Way. Orbiting M31 are at least 14 dwarf galaxies: the brightest and largest is M32, which can be seen with a basic telescope. The second brightest and closest one to M32 is M110. The other galaxies are fainter, and were mostly discovered only starting from the 1970s.

On January 11, 2006, it was announced that Andromeda Galaxy's faint companion galaxies lie on or close to a single plane running through the Andromeda Galaxy'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.

Table of known satellites[edit]

Andromeda Galaxy's satellites are listed here by discovery (orbital distance is not known).

Andromeda Galaxy's satellites
Name Type Distance from Sun
(million ly)
Right Ascension** Declination** Absolute Magnitude[1] Magnitude Mass-to-light ratio Year
discovered
Notes
M32 dE2 2.48 00h 42m 41.877s +40° 51′ 54.71″ +9.2 1749
M110 dE6 2.69 00h 40m 22.054s +41° 41′ 08.04″ +9.4 1773
NGC 185 dE5 2.01 00h 38m 57.523s +48° 20′ 14.86″ +11 1787
NGC 147 dE5 2.2 00h 33m 12.131s +48° 30′ 32.82″ +12 1829
Andromeda I dSph 2.43 00h 45m 39.264s +38° 02′ 35.17″ -11.8 +13.2 31 ± 6 [1] 1970
Andromeda II dSph 2.13 01h 16m 28.136s +33° 25′ 50.36″ -12.6 +13 13 ± 3 [1] 1970
Andromeda III dSph 2.44 00h 35m 31.777s +36° 30′ 04.19″ -10.2 +10.3 19 ± 12 [1] 1970
Andromeda IV * dIm? 22-24 00h 42m 32.798s +40° 34′ 16.27″   +16.6 1972 previously believed to be a satellite of Andromeda, but disproven in 2014.
Andromeda V dSph 2.52 01h 10m 16.952s +47° 37′ 40.12″ -9.6 +15.4 78 ± 50 [2] 1998
Pegasus Dwarf Spheroidal
(Andromeda VI)
dSph 2.55 23h 51m 46.516s +24° 34′ 55.69″ -11.5 +14.5 12 ± 5 [2] 1998
Cassiopeia Dwarf
(Andromeda VII)
dSph 2.49 23h 26m 33.321s +50° 40′ 49.98″ -13.3 +12.9 7.1 ± 2.8 [1] 1998
Andromeda VIII dSph 2.7 00h 42m 06s +40° 37′ 00″ +9.1 2003
Andromeda IX dSph 2.5 00h 52m 52.493s +43° 11′ 55.66″ -8.3 +16.2 2004
Andromeda X dSph 2.9 01h 06m 34.740s +44° 48′ 23.31″ -8.1 +16.2 63 ± 40 [1] 2005
Andromeda XI[3] dSph 00h 46m 20s +33° 48′ 05″ -7.3 2006
Andromeda XII[3] dSph 00h 47m 27s +33° 22′ 29″ -6.4 2006
Andromeda XIII[3] dSph 00h 51m 49.555s +33° 00′ 31.40″ -6.9 2006
Andromeda XIV[4] dSph 00h 41m 35.219s +29° 41′ 45.87″ -8.3 102 ± 71 [1] 2007
Andromeda XV[4] dSph 01h 14m 18.7s +38° 07′ 02.9″ -9.4 2007
Andromeda XVI[4] dSph 00h 59m 29.843s +32° 22′ 27.96″ -9.2 2007
Andromeda XVII[4] dSph 00h 37m 07s +44° 19′ 20″ -8.5 2008
Andromeda XVIII[4] dSph/Sm 00h 02m 15.184s +45° 05′ 19.78″ 2008
Andromeda XIX[4] dSph 00h 19m 32.1s +35° 02′ 37.1″ -9.3 2008
Andromeda XX[4] dSph 00h 07m 30.530s +35° 07′ 45.94″ -6.3 2008
Andromeda XXI[4] dSph 23h 54m 47.7s +42° 28′ 15″ -9.9 2009
Andromeda XXII[4] dSph 00h 27m 40s +28° 05′ 25″ -7.0 2009
Andromeda XXIII[4] dIrr 01h 29m 21.944s +38° 43′ 05.97″ 2011
Andromeda XXIV[4] 01h 18m 30s +46° 21′ 58″ 2011
Andromeda XXV[4] 00h 30m 08.9s +46° 51′ 07″ 2011
Andromeda XXVI[4] 00h 23m 45.6s +47° 54′ 58″ 2011
Andromeda XXVII[4] 00h 37m 27.1s +45° 23′ 13″ 2011
Andromeda XXVIII[5] dSph 22h 32m 41.449s +31° 12′ 59.10″ 2011
Andromeda XXIX[5] dIrr 23h 58m 55.440s +30° 45′ 22.09″ 2011
Tidal Stream Northwest
(Tidal Stream E and F)[6]
00h 20m 00s +46° 00′ 00″ 2009
Tidal Stream Southwest[6] 00h 30m 00s +37° 30′ 00″ 2009
Triangulum Galaxy*
(M33)
SA(s)cd 2.59 01h 33m 50.883s +30° 39′ 36.54″ +6.27 1654? Exact distance and relation to Andromeda uncertain

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

** RA/DEC values marked in Italics are rough estimates.

Interactions[edit]

Andromeda Galaxy (M31) seen 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 the latter's satellite galaxies, M32, blasted through one of the Andromeda Galaxy's spiral arms a few million years ago. Infrared pictures of the galaxy's two spiral arms demonstrate that they and the 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.

See also[edit]

References[edit]

External links[edit]