The Milky Way has several smaller galaxies gravitationally bound to it, as part of the Milky Way subgroup, which is part of the local galaxy cluster, the Local Group.
There are 61 small galaxies confirmed to be within of the Milky Way, but not all of them are necessarily in orbit, and some may themselves be in orbit of other satellite galaxies. The only ones visible to the naked eye are the Large and Small Magellanic Clouds, which have been observed since prehistory. Measurements with the Hubble Space Telescope in 2006 suggest the Magellanic Clouds may be moving too fast to be orbiting the Milky Way. Of the galaxies confirmed to be in orbit, the largest is the Sagittarius Dwarf Spheroidal Galaxy, which has a diameter of or roughly a twentieth that of the Milky Way.
Characteristics Satellite galaxies that orbit from of the edge of the disc of the Milky Way Galaxy to the edge of the dark matter halo of the Milky Way at from the center of the galaxy, are generally depleted in hydrogen gas compared to those that orbit more distantly. This is because of their interactions with the dense hot gas halo of the Milky Way that strip cold gas from the satellites. Satellites beyond that region still retain copious quantities of gas.
List The Milky Way's satellite galaxies include the following:
Name Diameter (kpc) Distance (kpc) Absolute visual magnitude Type Discovered Large Magellanic Cloud 4 48.5 −18.1 SBm prehistoric Antlia 2 2.9 130 −8.5 Irr? 2018 Sagittarius Dwarf 2.6 20 −13.5 E 1994 Crater II 2.2 117.5 −8.2 dSph 2016 Small Magellanic Cloud 2 61 −16.8 Irr prehistoric Canes Venatici I 1.1 220 −8.6 dSph 2006 Canis Major Dwarf 1.5 8 −14.4 Irr 2003 Boötes III 1.0 46 −5.75 dSph? 2009 Sculptor Dwarf 0.8 90 −11.1 dE3 1937 Draco Dwarf 0.7 80 −8.8 dE0 1954 Hercules 0.7 135 −6.6 dSph 2006 Leo II 0.7 210 −9.8 dE0 1950 Fornax Dwarf 0.6 140 −13.4 dE2 1938 Eridanus II 0.55 366 −7.1 dSph 2015 Sextans Dwarf Spheroidal 0.5 90 −9.3 dE3 1990 Carina Dwarf Spheroidal 0.5 100 −9.1 dE3 1977 Leo I 0.5 250 −12.0 dE3 1950 Ursa Minor Dwarf 0.4 60 −8.8 dE4 1954 Leo T 0.34 420 −8.0 dSph/dIrr 2006 Aquarius II 0.32 108 −4.2 dSph 2016 Boötes I 0.30 60 −6.3 dSph 2006 Canes Venatici II 0.30 155 −4.9 dSph 2006 Leo IV 0.30 160 −5.8 dSph 2006 Tucana IV 0.25 48 −3.5 dSph 2015 Columba I 0.21 182 −4.5 dSph 2015 Ursa Major II Dwarf 0.20 30 −4.25 dG D 2006 Grus II 0.19 53 −3.9 dSph 2015 Cetus III 0.18 251 −2.4 dSph? 2017 Coma Berenices 0.14 42 −4.1 dG D 2006 Hydra II 0.14 128 −4.8 dSph 2015 Reticulum III 0.13 92 −3.3 dSph 2015 Pisces II 0.12 180 −5.0 Sph 2010 Pegasus III 0.11 215 −3.4 dSph 2015 Hydrus I 0.10 28 −4.7 dSph 2018 Boötes II 0.10 42 −2.7 dSph 2007 Tucana III 0.09 25 −2.4 dSph 2015 Virgo I 0.09 91 −0.3 dSph 2016 Horologium II 0.09 78 −2.6 dSph 2015 Sagittarius II 0.08 67 −5.2 dSph 2015 Leo V 0.08 180 −5.2 dSph 2007 Triangulum II 0.07 30 −1.8 dSph 2015 Segue 2 0.07 35 −2.5 dSph 2007 Segue 1 0.06 23 −1.5 dSph 2007 Draco II 0.04 20 −2.9 dSph 2015 Tucana V 0.03 55 −1.6 dSph 2015 Cetus II 0.03 30 0.0 dSph? 2015 Reticulum II 0.064 30 −3.6 dSph 2015 Tucana II 0.33 70 −3.9 dSph 2015 Pisces Overdensity 1.5 80 −13 dSph? 2009 DES 1 0.02 82 −3.05 dSph? 2016 Eridanus III 0.028 90 −2.4 dSph? 2015 Horologium I 0.06 100 −3.5 dSph? 2015 Kim 2/Indus I 0.074 100 −3.5 GC/dSph 2015 Phoenix II 0.0521 100 −3.7 dSph? 2015 Ursa Major I Dwarf 0.64 100 −5.5 dG Sph 2005 Pictoris I 0.058 115 −3.7 dSph? 2015 Grus I 0.12 120 −3.4 dSph 2015 Pegasus IV 0.082 90 −4.25 dSph 2022 Carina II 0.182 36 −4.5 dSph 2018 Carina III 0.06 28 −2.4 GC? 2018 Boötes IV 0.28 209 −4.53 dSph 2019 Centaurus I 0.076 116 −5.55 dSph 2020 Pictor II 0.046 46 −3.2 dSph 2016 Boötes V 0.0194 102 −3.2 dSph? 2022 Leo Minor I 0.0897 82 −2.4 dSph 2022 Virgo II 0.07 72 −1.6 dSph 2022 Willman 1 0.02 38 −2.53 dSph 2018 Ursa Major III0.00310 +2.2dSph?2023 Leo K 0.0087 434 −4.86 dSph 2024 Leo M 0.009 459 −5.77 dSph 2024Sextans II 0.024? – – dSph2024Virgo III 0.015 154 – dSph2024Pegasus W0.01227 +1dSph2020Eridanus IV0.03459.7 +0.2dSph?2021Laevens 1 (Crater 1)0.0926.8 +0.8dG D2014Leo VI0.28111−3.56dSph2024Aquarius III0.10285−2.5dSph2024Aquarius IV 0.062 109 −1.9 dSph 2026
Map with clickable regions
Streams
The Sagittarius Dwarf Spheroidal Galaxy is currently in the process of being consumed by the Milky Way and is expected to pass through it within the next 100 million years. The Sagittarius Stream is a stream of stars in polar orbit around the Milky Way leeched from the Sagittarius Dwarf. The Virgo Stellar Stream is a stream of stars that is believed to have once been an orbiting dwarf galaxy that has been completely distended by the Milky Way's gravity.
See also List of Andromeda's satellite galaxies List of nearest galaxies Local Group
Notes
References
Further reading