Satellite galaxies of the Milky Way

Short description: Galaxies bound to 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 59 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.

## Contents

* 1 Characteristics
* 2 List
* 3 Map with clickable regions
* 4 Streams
* 5 See also
* 6 Notes
* 7 References
* 8 Further reading

## 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 Cloud | 4 | 48.5  | −18.1 | SBm | prehistoric
Antlia 2 | 2.9 | 130  | −8.5 | ? | 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  | - | 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
−7.1 | dSph | 2015 [9][10]
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 [11]
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 [12]
Columba I | 0.21 | 182  | −4.5 | dSph | 2015 [12]
Ursa Major II Dwarf | 0.20 | 30  | −4.25 | dG D | 2006
Grus II | 0.19 | 53  | −3.9 | dSph | 2015 [12]
Cetus III | 0.18 | 251  | −2.4 | dSph? | 2017 [13]
Coma Berenices | 0.14 | 42  | −4.1 | dSph | 2006
Hydra II | 0.14 | 128  | −4.8 | dSph | 2015 [14]
Reticulum III | 0.13 | 92  | −3.3 | dSph | 2015 [12]
Pisces II | 0.12 | 180  | −5.0 | dSph | 2010
Pegasus III | 0.11 | 215  | −3.4 | dSph | 2015 [15][16]
Hydrus I | 0.10 | 28  | −4.7 | dSph | 2018 [17]
Boötes II | 0.10 | 42  | −2.7 | dSph | 2007
Tucana III | 0.09 | 25  | −2.4 | dSph | 2015 [12]
Virgo I | 0.09 | 91  | −0.3 | dSph? | 2016 [13]
Horologium II | 0.09 | 78  | −2.6 | dSph | 2015 [18]
Sagittarius II | 0.08 | 67  | −5.2 | dSph | 2015 [19]
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 [19]
Tucana V | 0.03 | 55  | −1.6 | dSph | 2015 [12]
Cetus II | 0.03 | 30  | 0.0 | dSph? | 2015 [12]
Reticulum II | - | 30  | −3.6 | dSph | 2015 [9][10]
Tucana II | - | 70  | −3.9 | dSph | 2015 [9][10]
Pisces I | - | 80  | - | dSph? | 2009
DES 1 | - | 82  | - | GC | 2016 [20]
Eridanus III | - | 90  | −2.4 | dSph?[lower-alpha 2] | 2015 [9][10]
Horologium I | - | 100  | −3.5 | dSph?[lower-alpha 2] | 2015 [9][10]
Kim 2/Indus I | - | 100  | - | GC | 2015 [9][10]
Phoenix II | - | 100  | −3.7 | dSph?[lower-alpha 2] | 2015 [9][10]
Ursa Major I Dwarf | - | 100  | −5.5 | dG D | 2005
Pictoris I | - | 115  | −3.7 | dSph?[lower-alpha 2] | 2015 [9][10]
Grus I | - | 120  | −3.4 | dSph | 2015 [9]
Carina II | 0.182 | 36  | −4.5 | dSph | 2018 [21]
Carina III | 0.06 | 28  | −2.4 | GC? | 2018 [21]
Boötes IV | 0.28 | 209  | −4.53 | - | 2019 [22]
Centaurus I | 0.076 | 116  | −5.55 | - | 2020 [23]
Pictor II | 0.046 | 46  | −3.2 | - | 2016 [24]
Willman 1 | 0.02 | 38  | −2.53 | - | 2018 [25]

## Map with clickable regions

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## 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.

A side view to scale of Milky Way, its satellites, other major galaxies of the local group, smaller known galaxies, stellar streams, intergalactic dust clouds, and dark matter halos. The expected paths of the major members are indicated.

## 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, Rvir
2. ↑ 2.0 2.1 2.2 2.3 May be a globular cluster instead

## References

1. ↑ David G. Turner (15 August 2013). "An Eclectic View of our Milky Way Galaxy". Canadian Journal of Physics 92 (9): 959–963. September 2013. doi:10.1139/cjp-2013-0429. Bibcode: 2014CaJPh..92..959T.
2. ↑ "Press release: Magellanic Clouds May Be Just Passing Through". Harvard University. January 9, 2007. https://www.cfa.harvard.edu/news/2007-02.
3. ↑ Karachentsev, I. D.; Karachentseva, V. E.; Hutchmeier, W. K.; Makarov, D. I. (2004). "A Catalog of Neighboring Galaxies". The Astronomical Journal 127 (4): 2031–2068. doi:10.1086/382905. Bibcode: 2004AJ....127.2031K.
4. ↑ "Milky Way Ransacks Nearby Dwarf Galaxies". SpaceDaily. 17 October 2014. http://www.spacedaily.com/reports/Milky_Way_Ransacks_Nearby_Dwarf_Galaxies_Stripping_All_Traces_of_Star_Forming_Gas_999.html.
5. ↑ "Milky Way ransacks nearby dwarf galaxies". ScienceDaily. 15 October 2014. https://www.sciencedaily.com/releases/2014/10/141015152552.htm.
6. ↑ Sjölander, Nils. "Milky Way satellite galaxies". http://www.astro.uu.se/~ns/mwsat.html.
7. ↑ A. Drlica-Wagner (2020). "The Astrophysical Journal | Milky Way Satellite Census. I. The Observational Selection Function for Milky Way Satellites in DES Y3 and Pan-STARRS DR1". The Astrophysical Journal 893 (1): 47. doi:10.3847/1538-4357/ab7eb9. https://iopscience.iop.org/article/10.3847/1538-4357/ab7eb9.
8. ↑ Torrealba, G.; Koposov, S.E.; Belokurov, V.; Irwin, M. (13 April 2016). "The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater". Monthly Notices of the Royal Astronomical Society 459 (3): 2370–2378. doi:10.1093/mnras/stw733. Bibcode: 2016MNRAS.459.2370T.
9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 Koposov, Sergey E.; Belokurov, Vasily; Torrealba, Gabriel; Evans, N. Wyn (10 March 2015). "Beasts of the Southern Wild. Discovery of a large number of ultra faint satellites in the vicinity of the Magellanic Clouds". The Astrophysical Journal 805 (2): 130. doi:10.1088/0004-637X/805/2/130. Bibcode: 2015ApJ...805..130K.
10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 10.7 DES Collaboration (10 March 2015). "Eight New Milky Way companions discovered in first-year Dark Energy Survey data". The Astrophysical Journal 807 (1): 50. doi:10.1088/0004-637X/807/1/50. Bibcode: 2015ApJ...807...50B.
11. ↑ Torrealba, G.; Koposov, S.E.; Belokurov, V.; Irwin, M.; Collins, M.; Spencer, M.; Ibata, R.; Matteo, M. et al. (2016). "At the survey limits: Discovery of the Aquarius 2 dwarf galaxy in the VST ATLAS and the SDSS data". Monthly Notices of the Royal Astronomical Society 463 (1): 712–722. doi:10.1093/mnras/stw2051. Bibcode: 2016MNRAS.463..712T.
12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 12.6 Drlica-Wagner, A. (4 November 2015). "Eight ultra-faint galaxy candidates discovered in Year Two of the Dark Energy Survey". The Astrophysical Journal 813 (2): 109. doi:10.1088/0004-637X/813/2/109. Bibcode: 2015ApJ...813..109D.
13. ↑ 13.0 13.1 Homma, Daisuke; Chiba, Masashi; Okamoto, Sakurako; Komiyama, Yutaka; Tanaka, Masayuki; Tanaka, Mikito; Ishigaki, Miho N.; Hayashi, Kohei et al. (2017-04-19). "Searches for New Milky Way Satellites from the First Two Years of Data of the Subaru/Hyper Suprime-Cam Survey: Discovery of Cetus III". Publications of the Astronomical Society of Japan 70: S18. doi:10.1093/pasj/psx050. Bibcode: 2018PASJ...70S..18H.
14. ↑ Martin, Nicolas F. (23 April 2015). "Hydra II: A faint and compact Milky Way dwarf galaxy found in the survey of the Magellanic stellar history". The Astrophysical Journal Letters 804 (1): L5. doi:10.1088/2041-8205/804/1/L5. Bibcode: 2015ApJ...804L...5M.
15. ↑ Kim, Dongwon; Jerjen, Helmut; Mackey, Dougal; Da Costa, Gary S.; Milone, Antonino P. (12 May 2015). "A hero's dark horse: Discovery of an ultra-faint Milky Way satellite in Pegasus". The Astrophysical Journal Letters 804 (2): L-44. doi:10.1088/2041-8205/804/2/L44. Bibcode: 2015ApJ...804L..44K.
16. ↑ Kim, Dongwon; Jerjen, Helmut; Geha, Marla; Chiti, Anirudh; Milone, Antonino P.; Mackey, Dougal; da Costa, Gary; Frebel, Anna et al. (2016). "Portrait of a dark horse: Photometric properties and kinematics of the ultra-faint Milky Way satellite Pegasus III". The Astrophysical Journal 833 (1): 16. doi:10.3847/0004-637X/833/1/16. Bibcode: 2016ApJ...833...16K.
17. ↑ Koposov, Sergey E.; Walker, Matthew G.; Belokurov, Vasily; Casey, Andrew R.; Geringer-Sameth, Alex; Mackey, Dougal; Da Costa, Gary; Erkal, Denis et al. (2018-10-01). "Snake in the Clouds: a new nearby dwarf galaxy in the Magellanic bridge*" (in en). Monthly Notices of the Royal Astronomical Society 479 (4): 5343–5361. doi:10.1093/mnras/sty1772. ISSN 0035-8711.
18. ↑ Kim, Dongwon; Jerjen, Helmut (28 July 2015). "Horologium II: A second ultra-faint Milky Way satellite in the Horologium constellation". The Astrophysical Journal Letters 808 (2): L-39. doi:10.1088/2041-8205/808/2/L39. Bibcode: 2015ApJ...808L..39K.
19. ↑ 19.0 19.1 Laevens, B.P.M; Martin, N.F.; Bernard, E.J.; Schlafly, E.F.; Sesar, B. (1 November 2015). "Sagittarius II, Draco II and Laevens 3: Three new Milky Way satellites discovered in the PAN-STARRS 1 3π survey". The Astrophysical Journal 813 (1): 44. doi:10.1088/0004-637X/813/1/44. Bibcode: 2015ApJ...813...44L.
20. ↑ Luque, E. (9 February 2016). "Digging deeper into Southern skies: A compact Milky Way companion discovered in first-year Dark Energy Survey data". Monthly Notices of the Royal Astronomical Society 458 (1): 603–612. doi:10.1093/mnras/stw302. Bibcode: 2016MNRAS.458..603L.
21. ↑ 21.0 21.1 Torrealba, G.; Belokurov, V.; Koposov, S. E.; Bechtol, K.; Drlica-Wagner, A.; Olsen, K. A. G.; Vivas, A. K.; Yanny, B. et al. (2018-01-22). "Discovery of two neighbouring satellites in the Carina constellation with MagLiteS". Monthly Notices of the Royal Astronomical Society 475 (4): 5085–5097. doi:10.1093/mnras/sty170.
22. ↑ Homma (2019). "Boötes. IV. A new Milky Way satellite discovered in the Subaru Hyper Suprime-Cam Survey and implications for the missing satellite problem". Publications of the Astronomical Society of Japan 71 (5). doi:10.1093/pasj/psz076. https://academic.oup.com/pasj/article-abstract/71/5/94/5539816.
23. ↑ Mau (2020). "Two Ultra-faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey". The Astrophysical Journal 890 (2): 136. doi:10.3847/1538-4357/ab6c67. Bibcode: 2020ApJ...890..136M. https://iopscience.iop.org/article/10.3847/1538-4357/ab6c67.
24. ↑ Drlica-Wagner (2016). "An Ultra-Faint Galaxy Candidate Discovered in Early Data from the Magellanic Satellites Survey". The Astrophysical Journal 833 (1): L5. doi:10.3847/2041-8205/833/1/L5. Bibcode: 2016ApJ...833L...5D. https://iopscience.iop.org/article/10.3847/2041-8205/833/1/L5.
25. ↑ Muñoz (2018). "A MegaCam Survey of Outer Halo Satellites. III. Photometric and Structural Parameters". The Astrophysical Journal 860 (1): 66. doi:10.3847/1538-4357/aac16b. Bibcode: 2018ApJ...860...66M. https://iopscience.iop.org/article/10.3847/1538-4357/aac16b.

## 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): L5. 13 October 2014. doi:10.1088/2041-8205/795/1/L5. Bibcode: 2014ApJ...795L...5S.

* v
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The Milky Way

Location|

Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Observable universe → Universe
Each arrow (→) may be read as "within" or "part of".

Galactic core|

* Center of the Milky Way
* Sagittarius A
* Sagittarius A*
* Supermassive black hole

Spiral arms|

* Carina–Sagittarius
* Norma–Cygnus
* Orion–Cygnus
* Perseus
* Scutum–Centaurus

Satellite galaxies|

| Magellanic Clouds|

* Large Magellanic Cloud
* Small Magellanic Cloud
* Magellanic Stream
* Magellanic Bridge

|

Sagittarius Spheroidal|

* Sagittarius Stream
* Boötes II
* Coma Berenices
* Messier 54
* Palomar 12
* Segue 1
* Segue 2
* Terzan 7

Dwarfs|

* Antlia 2
* Boötes I
* Boötes III
* Canes Venatici I
* Canes Venatici II
* Canis Major
* Carina
* Crater 2
* Draco
* Fornax
* Hercules
* Leo I
* Leo II
* Leo IV
* Leo V
* Leo T
* Phoenix
* Pisces I
* Pisces II
* Sculptor
* Sextans
* Triangulum II
* Ursa Major I
* Ursa Major II
* Ursa Minor
* Virgo I

Other|

* Gaia Sausage
* Monoceros Ring
* Virgo Stream
* Koposov I
* Koposov II
* Segue 3
* Willman 1

Related|

* Andromeda–Milky Way collision
* Baade's Window

Astronomy portal

*[980,000 ly (300 kpc)]: virial radius of our galaxy
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