Satellite galaxies of the Milky Way

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.[1]

There are 69 small galaxies confirmed to be within 420 kiloparsecs (1.4 million light-years) 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.[2] Of the galaxies confirmed to be in orbit, the largest is the Sagittarius Dwarf Elliptical Galaxy, which has a diameter of 2.6 kiloparsecs (8,500 ly)[3] or roughly a twentieth that of the Milky Way.

Characteristics

Satellite galaxies that orbit from 1,000 ly (310 pc) of the edge of the disc of the Milky Way Galaxy to the edge of the dark matter halo of the Milky Way at 980,000 ly (300 kpc) from the center of the galaxy,[lower-alpha 1] 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.[4][5]

List

The Milky Way's satellite galaxies include the following:[6][7]

Name Diameter (kpc) Distance
(kpc)		 Absolute visual magnitude Type Discovered
Large Magellanic Cloud448.5 −18.1SBmprehistoric
Antlia 22.9 130 −8.5Irr?2018
Sagittarius Dwarf2.620 −13.5E1994
Crater II2.2117.5 −8.2dSph2016 [8]
Small Magellanic Cloud261 −16.8Irrprehistoric
Canes Venatici I1.1220 −8.6dSph2006
Canis Major Dwarf1.58 −14.4Irr2003
Boötes III1.046 −5.75dSph?2009
Sculptor Dwarf0.890 −11.1dE31937
Draco Dwarf0.780 −8.8dE01954
Hercules0.7135 −6.6dSph2006
Leo II0.7210 −9.8dE01950
Fornax Dwarf0.6140 −13.4dE21938
Eridanus II[9]0.55366 −7.1dSph2015 [10][11]
Sextans Dwarf Spheroidal0.590 −9.3dE31990
Carina Dwarf Spheroidal0.5100 −9.1dE31977
Leo I0.5250 −12.0dE31950
Ursa Minor Dwarf0.460 −8.8dE41954
Leo T0.34420 −8.0dSph/dIrr2006
Aquarius II0.32108 −4.2dSph2016 [12]
Boötes I0.3060 −6.3dSph2006
Canes Venatici II0.30155 −4.9dSph2006
Leo IV0.30160 −5.8dSph2006
Tucana IV0.2548 −3.5dSph2015 [13]
Columba I0.21182 −4.5dSph2015 [13]
Ursa Major II Dwarf0.2030 −4.25dG D2006
Grus II0.1953 −3.9dSph2015 [13]
Cetus III0.18251 −2.4dSph?2017 [14]
Coma Berenices0.1442 −4.1dSph2006
Hydra II0.14128 −4.8dSph2015 [15]
Reticulum III0.1392 −3.3dSph2015 [13]
Pisces II0.12180 −5.0dSph2010
Pegasus III0.11215 −3.4dSph2015 [16][17]
Hydrus I0.1028 −4.7dSph2018 [18]
Boötes II0.1042 −2.7dSph2007
Tucana III0.0925 −2.4dSph2015 [13]
Virgo I0.0991 −0.3dSph?2016 [14]
Horologium II0.0978 −2.6dSph2015 [19]
Sagittarius II0.0867 −5.2dSph2015 [20]
Leo V0.08180 −5.2dSph2007
Triangulum II0.0730 −1.8dSph2015
Segue 20.0735 −2.5dSph2007
Segue 10.0623 −1.5dSph2007
Draco II0.0420 −2.9dSph2015 [20]
Tucana V0.0355 −1.6dSph2015 [13]
Cetus II0.0330 0.0dSph?2015 [13]
Reticulum II0.06430 −3.6dSph2015 [10][11]
Tucana II0.3370 −3.9dSph2015 [10][11]
Pisces Overdensity1.580 −13dSph?2009
DES 10.0282 −3.05GC2016 [21]
Eridanus III0.02890 −2.4dSph?[lower-alpha 2]2015 [10][11]
Horologium I0.06100 −3.5dSph?[lower-alpha 2]2015 [10][11]
Kim 2/Indus I0.074100 −3.5GC2015 [10][11]
Phoenix II0.0521100 −3.7dSph?[lower-alpha 2]2015 [10][11]
Ursa Major I Dwarf0.64100 −5.5dG D2005
Pictoris I0.058115 −3.7dSph?[lower-alpha 2]2015 [10][11]
Grus I0.12120 −3.4dSph2015 [10]
Pegasus IV0.08290 −4.25dSph2022 [22]
Carina II0.18236 −4.5dSph2018 [23]
Carina III0.0628 −2.4GC?2018 [23]
Boötes IV0.28209 −4.53dSph2019 [24]
Centaurus I0.076116 −5.55dSph2020 [25]
Pictor II0.04646 −3.2dSph2016 [26]
Willman 10.0238 −2.53dSph2018 [27]

Map with clickable regions
Milky Way's satellite galaxies (clickable map)

Streams
See also: List of stellar 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

Notes
  1. The distance to edge of the dark matter halo of the galaxy from its center is the virial radius of a galaxy, Rvir
  2. May be a globular cluster instead

    References
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    Further reading
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