Local Group

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Local Group of galaxies, including the massive members Messier 31 (Andromeda Galaxy) and Milky Way, as well as other nearby galaxies.
Distribution of the iron content (in logarithmic scale) in four dwarf neighbouring galaxies of the Milky Way

The Local Group is the galaxy group that includes the Milky Way. The Local Group comprises more than 54 galaxies, most of them dwarf galaxies. Its gravitational center is located somewhere between the Milky Way and the Andromeda Galaxy. The Local Group has a diameter of 10 Mly (3.1 Mpc) (about 1023 meters) and has a binary (dumbbell)[1] distribution. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster.

The three largest members of the group (in descending order) are the Andromeda Galaxy, the Milky Way[2] and the Triangulum Galaxy. The larger two of these spiral galaxies each have their own system of satellite galaxies.


The term "The Local Group" was introduced by Edwin Hubble in Chapter VI of his 1936 book The Realm of the Nebulae.[7] There, he described it as "a typical small group of nebulae which is isolated in the general field" and delineated, by decreasing luminosity, its members to be M31, Milky Way, M33, Large Magellanic Cloud, Small Magellanic Cloud, M32, NGC 205, NGC 6822, NGC 185, IC 1613 and NGC 147. He also identified IC 10 as a possible part of Local Group.

By 2003, the number of known Local Group members had increased from his initial 12 to 36.[8]

Component galaxies[edit]


Sextans BSextans AMilky WayLeo I (dwarf galaxy)Canes DwarfLeo II (dwarf galaxy)NGC 6822Phoenix DwarfTucana DwarfWolf-Lundmark-MelotteCetus DwarfIC 1613SagDIGAquarius DwarfTriangulum GalaxyNGC 185NGC 147IC 10Andromeda GalaxyM110Leo ANGC 3109Antlia DwarfLGS 3Pegasus DwarfAndromeda IIAndromeda IIIAndromeda I
About this image
Local Group (clickable map)

List of galactic bodies[edit]

Spiral galaxies
name type constellation notes
Andromeda Galaxy (M31, NGC 224) SA(s)b Andromeda ~220 kly in diameter, it is the largest and most massive galaxy in the group.
Milky Way SBbc Sagittarius (centre) As large as Andromeda galaxy, between 150 and 180kly, home 500-580 billion stars .[9][10]
Triangulum Galaxy (M33, NGC 598) SA(s)cd Triangulum Third largest, only unbarred spiral galaxy and possible satellite of the Andromeda Galaxy. Triangulum Galaxy has mass of ~50 billion solar masses and is Home to ~60 billion stars.
Elliptical galaxies
name type constellation notes
M32 (NGC 221) E2 Andromeda satellite of the Andromeda Galaxy
Irregular galaxies
name type constellation notes
Wolf–Lundmark–Melotte (WLM, DDO 221) Ir+ Cetus
IC 10 KBm or Ir+ Cassiopeia
Small Magellanic Cloud (SMC, NGC 292) SB(s)m pec Tucana satellite of Milky Way, 6th largest galaxy in the local group with mass of between 7.5 and 8 billion solar mass.
Canis Major Dwarf Irr Canis Major satellite of Milky Way
Pisces Dwarf (LGS3) Irr Pisces satellite of the Triangulum Galaxy?
IC 1613 (UGC 668) IAB(s)m V Cetus
Phoenix Dwarf Irr Phoenix
Large Magellanic Cloud (LMC) Irr/SB(s)m Dorado Fourth largest member of the group, satellite of Milky Way, mass between 10 and 85 billion solar masses. Recent finding puts it at 10% mass of Milky Way Galaxy.[11]
Leo A (Leo III) IBm V Leo
Sextans B (UGC 5373) Ir+IV-V Sextans
NGC 3109 Ir+IV-V Hydra
Sextans A (UGCA 205) Ir+V Sextans
Aquarius Dwarf (DDO 210) IB(s)m Aquarius Distance 3.2 million light years. Quite isolated in space, membership to Local Group established in 1999[12]
Dwarf elliptical galaxies
name type constellation notes
M110 (NGC 205) dE6p Andromeda satellite of the Andromeda Galaxy and 5th largest galaxy with the mass of 9.3 billion solar masses.
NGC 147 (DDO 3) dE5 pec Cassiopeia satellite of the Andromeda Galaxy
SagDIG (Sagittarius Dwarf Irregular Galaxy) IB(s)m V Sagittarius Most remote from barycenter member thought to be in the Local Group.[12]
NGC 6822 (Barnard's Galaxy) IB(s)m IV-V Sagittarius
Pegasus Dwarf (Pegasus Dwarf Irregular, DDO 216) Irr Pegasus
Dwarf spheroidal galaxies
name type constellation notes
Boötes I dSph Boötes
Cetus Dwarf dSph/E4 Cetus
Canes Venatici I Dwarf and Canes Venatici II Dwarf dSph Canes Venatici
KKs 3 dSph
Andromeda III dE2 Andromeda satellite of the Andromeda Galaxy
NGC 185 dE3 pec Cassiopeia satellite of the Andromeda Galaxy
Andromeda I dE3 pec Andromeda satellite of the Andromeda Galaxy
Sculptor Dwarf (E351-G30) dE3 Sculptor satellite of Milky Way
Andromeda V dSph Andromeda satellite of the Andromeda Galaxy
Andromeda II dE0 Andromeda satellite of the Andromeda Galaxy
Fornax Dwarf (E356-G04) dSph/E2 Fornax satellite of Milky Way
Carina Dwarf (E206-G220) dE3 Carina satellite of Milky Way
Antlia Dwarf dE3/dSph/Irr? Antlia
Leo I (DDO 74) dE3 Leo satellite of Milky Way
Sextans Dwarf dE3 Sextans satellite of Milky Way
Leo II (Leo B) dE0 pec Leo satellite of Milky Way
Ursa Minor Dwarf dE4 Ursa Minor satellite of Milky Way
Draco Dwarf (DDO 208) dE0 pec Draco satellite of Milky Way
SagDSG (Sagittarius Dwarf Spheroidal Galaxy) dSph/E7 Sagittarius satellite of Milky Way
Tucana Dwarf dE5 Tucana
Cassiopeia Dwarf (Andromeda VII) dSph Cassiopeia satellite of the Andromeda Galaxy
Pegasus Dwarf Spheroidal Galaxy (Andromeda VI) dSph Pegasus satellite of the Andromeda Galaxy
Ursa Major I Dwarf and Ursa Major II Dwarf dSph Ursa Major satellite of Milky Way
Leo IV dSph Leo satellite of the Milky Way
Leo V dSph Leo satellite of the Milky Way
Leo T dSph/Irr Leo satellite of the Milky Way
Boötes II dSph Boötes satellite of the Milky Way
Boötes III dSph Boötes satellite of the Milky Way
Coma Berenices dSph Coma Berenices satellite of the Milky Way
Segue 2 dSph Aries satellite of the Milky Way
Hercules dSph Hercules satellite of the Milky Way
Pisces II dSph Pisces satellite of the Milky Way
Reticulum II dSph Reticulum satellite of the Milky Way
Eridanus II dSph Eridanus probable satellite of the Milky Way
Grus dSph Grus satellite of the Milky Way
Tucana II dSph Tucana satellite of the Milky Way
Identification unclear
name type constellation notes
Virgo Stellar Stream dSph (remnant)? Virgo In the process of merging with the Milky Way
Willman 1 dSph or Globular Cluster Ursa Major 147,000 light-years away
UGCA 86 (0355+66) Irr, dE or S0 Camelopardalis
UGCA 92 (EGB0427+63) Irr or S0 Camelopardalis
Horologium dSph or Globular Cluster Horologium satellite of the Milky Way. Not to be confused with the Horologium Supercluster.
Pictoris dSph or Globular Cluster Pictor satellite of the Milky Way
Phoenix II dSph or Globular Cluster Phoenix satellite of the Milky Way
Indus dSph or Globular Cluster Indus satellite of the Milky Way
Eridanus III dSph or Globular Cluster Eridanus satellite of the Milky Way
Probable non-members
name type constellation notes
GR 8 (DDO 155) Im V Virgo Distance 7.9 million light years[13]
IC 5152 IAB(s)m IV Indus Distance 5.8 million light years, possibly an outlying member of the local group[14]
NGC 55 SB(s)m Sculptor Distance 7.2 million light years[15]
NGC 404 E0 or SA(s)0 Andromeda Distance 10 million light years[16]
Andromeda IV Irr Andromeda Once considered to be associated with M31. Its distance is now known to be 22 to 24 million light years (not close to the Andromeda Galaxy at all).[17]
NGC 1569 Irp+ III-IV Camelopardalis In IC 342 group of galaxies. Distance 11 million light years[18]
NGC 1560 (IC 2062) Sd Camelopardalis Distance 8-12 million light years
Camelopardalis A Irr Camelopardalis
Argo Dwarf Irr Carina
ESO 347-8 (2318–42) Irr Grus
UKS 2323-326 Irr Sculptor
UGC 9128 (DDO 187) Irp+ Boötes
Objects in the Local Group no longer recognised as galaxies
name type constellation notes
Palomar 12 (Capricornus Dwarf) Capricornus a globular cluster formerly classified as a dwarf spheroidal galaxy
Palomar 4 (Ursa Major Dwarf) Ursa Major a globular cluster formerly classified as a dwarf spheroidal galaxy
Palomar 3 (Sextans C) Sculptor a globular cluster formerly classified as a dwarf spheroidal galaxy[19]

Other objects[edit]

A diagram of our location in the observable universe. (Alternative image.)

See also[edit]


  1. ^ a b Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics. 49 (1): 3–18. Bibcode:2006Ap.....49....3K. doi:10.1007/s10511-006-0002-6.
  2. ^ "The Local Group". NASA's High Energy Astrophysics Science Archive Research Center (HEASARC). NASA. Retrieved 2015-05-05.
  3. ^ Kalirai, Jason S.; Beaton, Rachael L.; Geha, Marla C.; Gilbert, Karoline M.; Guhathakurta, Puragra; Kirby, Evan N.; Majewski, Steven R.; Ostheimer, James C.; Patterson, Richard J. (2010-02-17). "THE SPLASH SURVEY: INTERNAL KINEMATICS, CHEMICAL ABUNDANCES, AND MASSES OF THE ANDROMEDA I, II, III, VII, X, AND XIV DWARF SPHEROIDAL GALAXIES,". The Astrophysical Journal. 711 (2): 671–692. doi:10.1088/0004-637X/711/2/671. ISSN 0004-637X.
  4. ^ Sergey E. Koposov; Vasily Belokurov; Gabriel Torrealba; N. Wyn Evans (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: 130. arXiv:1503.02079. Bibcode:2015ApJ...805..130K. doi:10.1088/0004-637X/805/2/130.
  5. ^ Miller, Bryan W.; et al. (December 2001), "The Star Formation History of LGS 3", The Astrophysical Journal, 562 (2): 713–726, arXiv:astro-ph/0108408, Bibcode:2001ApJ...562..713M, doi:10.1086/323853
  6. ^ "The observed properties of dwarf galaxies in and around the Local Group" (PDF).
  7. ^ Hubble, E.P. (1936). The realm of the nebulae. Mrs. Hepsa Ely Silliman memorial lectures, 25. New Haven: Yale University Press. ISBN 9780300025002. OCLC 611263346. Archived from the original on 2012-09-29.(pp. 124–151)
  8. ^ van den Bergh, Sidney (May 2003). "History of the Local Group". To be published in: "The Local Group as an Astrophysical Laboratory". Cambridge University Press: 5042. arXiv:astro-ph/0305042. Bibcode:2003astro.ph..5042V.
  9. ^ http://www.atlasoftheuniverse.com/galaxies.html
  10. ^ https://arxiv.org/abs/1503.00257
  11. ^ http://www.cam.ac.uk/research/news/a-bridge-of-stars-connects-two-dwarf-galaxies
  12. ^ a b van den Bergh, Sidney (April 2000). "Updated Information on the Local Group". The Publications of the Astronomical Society of the Pacific. 112 (770): 529–536. arXiv:astro-ph/0001040. Bibcode:2000PASP..112..529V. doi:10.1086/316548.
  13. ^ Tolstoy, Eline (1999). "Detailed Star-Formation Histories of Nearby Dwarf Irregular Galaxies using HST". In Patricia Whitelock and Russell Cannon. The stellar content of Local Group galaxies, Proceedings of the 192nd symposium of the International Astronomical Union. Astronomical Society of the Pacific. p. 218. Bibcode:1999IAUS..192..218T. ISBN 1886733821.
  14. ^ Ziljstra, A. A.; Minniti, Dante (April 1999). "A Dwarf Irregular Galaxy at the Edge of the Local Group: Stellar Populations and Distance of IC 5152". Astronomical Journal. 117 (4): 1743–1757. arXiv:astro-ph/9812330. Bibcode:1999AJ....117.1743Z. doi:10.1086/300802. Retrieved 2011-03-11.
  15. ^ van de Steene, G. C.; et al. (2006). "Distance determination to NGC 55 from the planetary nebula luminosity function". Astronomy and Astrophysics. 455 (3): 891–896. Bibcode:2006A&A...455..891V. doi:10.1051/0004-6361:20053475.
  16. ^ Jensen, Joseph B.; Tonry, John L.; Barris, Brian J.; Thompson, Rodger I.; et al. (February 2003). "Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations". Astrophysical Journal. 583 (2): 712–726. arXiv:astro-ph/0210129. Bibcode:2003ApJ...583..712J. doi:10.1086/345430.
  17. ^ Nowakowski, Tomasz (22 December 2015). "Andromeda IV turns out to be a solitary gas-rich dwarf galaxy". physorg. Retrieved 25 December 2015.
  18. ^ Grocholski, Aaron J.; Aloisi, Alessandra; van der Marel, Roeland P.; Mack, Jennifer; et al. (October 20, 2008). "A New Hubble Space Telescope Distance to NGC 1569: Starburst Properties and IC 342 Group Membership". Astrophysical Journal Letters. 686 (2): L79–L82. arXiv:0808.0153. Bibcode:2008ApJ...686L..79G. doi:10.1086/592949.
  19. ^ "Pal3". simbad.u-strasbg.fr. Retrieved 26 August 2017.
  20. ^ Wakker, B. P.; York, D. G.; Wilhelm, R.; Barentine, J. C.; Richter, P.; Beers, T. C.; Ivezić, Ž.; Howk, J. C. (2008). "Distances to Galactic High‐Velocity Clouds. I. Cohen Stream, Complex GCP, Cloud g1". The Astrophysical Journal. 672 (1): 298–319. arXiv:0709.1926. Bibcode:2008ApJ...672..298W. doi:10.1086/523845.
  21. ^ "Massive Gas Cloud Speeding Toward Collision With Milky Way". Retrieved 2008-06-06.

External links[edit]