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 61 small galaxies confirmed to be within 420 kiloparsecs (1.4 million light-years) of the Milky Way,^[2] 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.^[3] 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)^[4] 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.^[5][6]

List

The Milky Way's satellite galaxies include the following:^[7][2]

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 [8]
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[9]	0.55	366	−7.1	dSph	2015 [10][11]
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 [12]
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 [13]
Columba I	0.21	182	−4.5	dSph	2015 [13]
Ursa Major II Dwarf	0.20	30	−4.25	dG D	2006
Grus II	0.19	53	−3.9	dSph	2015 [13]
Cetus III	0.18	251	−2.4	dSph?	2017 [14]
Coma Berenices	0.14	42	−4.1	dSph	2006
Hydra II	0.14	128	−4.8	dSph	2015 [15]
Reticulum III	0.13	92	−3.3	dSph	2015 [13]
Pisces II	0.12	180	−5.0	dSph	2010
Pegasus III	0.11	215	−3.4	dSph	2015 [16][17]
Hydrus I	0.10	28	−4.7	dSph	2018 [18]
Boötes II	0.10	42	−2.7	dSph	2007
Tucana III	0.09	25	−2.4	dSph	2015 [13]
Virgo I	0.09	91	−0.3	dSph?	2016 [14]
Horologium II	0.09	78	−2.6	dSph	2015 [19]
Sagittarius II	0.08	67	−5.2	dSph	2015 [20]
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 [20]
Tucana V	0.03	55	−1.6	dSph	2015 [13]
Cetus II	0.03	30	0.0	dSph?	2015 [13]
Reticulum II	0.064	30	−3.6	dSph	2015 [10][11]
Tucana II	0.33	70	−3.9	dSph	2015 [10][11]
Pisces Overdensity	1.5	80	−13	dSph?	2009
DES 1	0.02	82	−3.05	GC	2016 [21]
Eridanus III	0.028	90	−2.4	dSph?[lower-alpha 2]	2015 [10][11]
Horologium I	0.06	100	−3.5	dSph?[lower-alpha 2]	2015 [10][11]
Kim 2/Indus I	0.074	100	−3.5	GC	2015 [10][11]
Phoenix II	0.0521	100	−3.7	dSph?[lower-alpha 2]	2015 [10][11]
Ursa Major I Dwarf	0.64	100	−5.5	dG D	2005
Pictoris I	0.058	115	−3.7	dSph?[lower-alpha 2]	2015 [10][11]
Grus I	0.12	120	−3.4	dSph	2015 [10]
Pegasus IV	0.082	90	−4.25	dSph	2022[22]
Carina II	0.182	36	−4.5	dSph	2018 [23]
Carina III	0.06	28	−2.4	GC?	2018 [23]
Boötes IV	0.28	209	−4.53	dSph	2019 [24]
Centaurus I	0.076	116	−5.55	dSph	2020 [25]
Pictor II	0.046	46	−3.2	dSph	2016 [26]
Boötes V	-	102	−3.2	-	2022[27]
Leo Minor I	-	82	−2.4	-	2022[27]
Virgo II	-	72	−1.6	-	2022[27]
Willman 1	0.02	38	−2.53	dSph	2018 [28]
Ursa Major III	0.003	10	+2.2	dSph	2023
Leo K	-	434	−4.86	dSph	2024[29]
Leo M	-	459	−5.77	dSph	2024[29]
Sextans II	-	-	-	-	2024[30]
Virgo III	-	154[31]	-	-	2024[30]

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

• List of Andromeda's satellite galaxies
• List of nearest galaxies
• Local Group

Notes

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

References

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Further reading

• K. Spekkens; N. Urbancic; B. S. Mason; B. Willman; J. E. Aguirre (30 September 2014). "The Dearth of Neutral Hydrogen in Galactic Dwarf Spheroidal Galaxies". The Astrophysical Journal Letters. 795 (1) (published 13 October 2014): L5. arXiv:1410.0028. Bibcode:2014ApJ...795L...5S. doi:10.1088/2041-8205/795/1/L5. S2CID 35113298.