The Andromeda Galaxy (M31) has satellite galaxies just like the Milky Way. Orbiting M31 are at least 35 dwarf galaxies: the brightest and largest is M110, which can be seen with a basic telescope. The second-brightest and closest one to M31 is M32. The other galaxies are fainter, and were mostly discovered 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.
It is unknown whether the Triangulum Galaxy is a satellite of Andromeda.
Table of known satellites Andromeda Galaxy's satellites are listed here by discovery (orbital distance is not known). Andromeda IV is not included in the list, as it was discovered to be roughly 10 times further than Andromeda from the Milky Way in 2014, and therefore a completely unrelated galaxy.
+ Andromeda Galaxy's satellites Name Type Distance from Sun(million ly) Right Ascension Declination Absolute Magnitude Apparent magnitude Mass-to-light ratio 3D distance to M31 (kly) Yeardiscovered Notes M32 dE2 2.48 +8.1 1749 M110 dE6 2.69 −16.5 +8.5 1773 NGC 185 dE5 2.01 +10.1 1787 NGC 147 dE5 2.2 +10.5 1829 Andromeda I dSph 2.43 −11.8 +13.6 31 ± 6 1970 Andromeda II dSph 2.13 −12.6 +13.5 13 ± 3 1970 Andromeda III dSph 2.44 −10.2 +15.0 19 ± 12 1970 Andromeda V dSph 2.52 −9.6 +15.9 78 ± 50 1998 Pegasus Dwarf Spheroidal(Andromeda VI) dSph 2.55 −11.5 +14.2 12 ± 5 1998 Cassiopeia Dwarf(Andromeda VII) dSph 2.49 −13.3 +12.9 7.1 ± 2.8 1998 Andromeda VIII dSph 2.7 +9.1 2003 Tidally disrupting; identification unclear Andromeda IX dSph 2.5 −8.3 +16.2 127.2 2004 Andromeda X dSph 2.9 −8.1 +16.1 63 ± 40 332.7 2005 Andromeda XI dSph −7.3 2006 Andromeda XII dSph −6.4 2006 Andromeda XIII (Pisces III) dSph −6.9 2006 Andromeda XIVDiscovery of the Local Group Galaxies (Pisces IV) dSph −8.3 102 ± 71 2007 Andromeda XV dSph −9.4 2007 Andromeda XVI (Pisces V) dSph 2.143 −9.2 580.6 2007 Andromeda XVII dSph −8.5 313.1 2008 Andromeda XVIII dSph/Sm 515.3 2008 Andromeda XIX dSph −9.3 2008 Andromeda XX dSph −6.3 512.1 2008 Andromeda XXI dSph −9.9 472.9 2009 Andromeda XXII dSph −7.0 910 2009 Andromeda XXIII dIrr 427.3 2011 Andromeda XXIV 401.2 2011 Andromeda XXV 319.6 2011 Andromeda XXVI 489.2 2011 Andromeda XXVII 2011 Tidally disrupted Andromeda XXVIII (reprinted in R&D Magazine) dSph −8.8 2011 Andromeda XXIX dIrr 636 2011 Andromeda XXX (Cassiopeia II) dSph? Andromeda XXXI (Lacerta I) dSph? 2013 Andromeda XXXII (Cassiopeia III) dSph? 2.74 508 2013 Andromeda XXXIII (Perseus I) dSph? 2.41 1,140 2013 Andromeda XXXVIdSph01 16 39.91 +47 39 13.364 ±303882026A ultra-faint galaxy. Possibly the second most compact satellite of Andromeda. Tidal Stream Northwest (Tidal Stream E and F)New tidal streams found in Andromeda reveal history of galactic mergers 2009 Tidal Stream Southwest 2009 Pegasus V galaxy (Peg V, Andromeda XXXIV) d ±0.1 ±3 −6.3 2022 Andromeda XXXV3.02 -5.22025 Triangulum Galaxy(M33) SA(s)cd 2.59 +6.27 750 1654? Its relation to Andromeda is uncertain.
See also Satellite galaxies of the Milky Way List of nearest galaxies Local Group
References
External links Andromeda's thin sheet of satellites – Dark matter filiments or galaxtic cannibalism? Strange Setup: Andromeda's Satellite Galaxies All Lined Up