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A member of the Local Group of galaxies, irregular galaxy Sextans A is 4.3 million light-years distant. The bright Milky Way foreground stars appear yellowish in this view. Beyond them lie the stars of Sextans A with young blue star clusters clearly visible.

Distribution of the iron content (in logarithmic scale) in four dwarf neighbouring galaxies of the Milky Way.

The Local Group is the group of galaxies that includes our galaxy, the Milky Way. The group comprises about 30 galaxies (including dwarf galaxies), with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy. The galaxies of the Local Group cover a 10 million light-year diameter (see 1 E+22 m for distance comparisons) and have a binary (dumbbell)^[1] shape. The group is estimated to have a total mass of (1.29 ± 0.14) × 10¹²M_☉.^[1] The group itself is one of many within the Virgo Supercluster (i.e. the Local Supercluster).^[2]

The two most massive members of the group are the Milky Way and the Andromeda Galaxy. These two Spiral Galaxies each have a system of satellite galaxies.

• The Milky Way's satellite system consists of Sagittarius Dwarf Galaxy, Large Magellanic Cloud, Small Magellanic Cloud, Canis Major Dwarf, Ursa Minor Dwarf, Draco Dwarf, Carina Dwarf, Sextans Dwarf, Sculptor Dwarf, Fornax Dwarf, Leo I, Leo II, and Ursa Major Dwarf.
• Andromeda's satellite system comprises M32, M110, NGC 147, NGC 185, And I, And II, And III, And IV, And V, Pegasus dSph, Cassiopeia Dwarf, And VIII, And IX, and And X.
• The Triangulum Galaxy, the third largest and only other ordinary spiral galaxy in the Local Group, may or may not be a companion to the Andromeda galaxy but probably has Pisces Dwarf as a satellite.

The other members of the group are gravitationally secluded from these large subgroups: IC10, IC1613, Phoenix Dwarf, Leo A, Tucana Dwarf, Cetus Dwarf, Pegasus Dwarf Irregular, Wolf-Lundmark-Melotte, Aquarius Dwarf, and Sagittarius Dwarf Irregular.

History

The term "The Local Group" was introduced by Edwin Hubble in Chapter VI of his book The Realm of the Nebulae (Hubble 1936, pp. 124–151). There he describes it as "a typical small group of nebulae which is isolated in the general field." In that book he delineated by decreasing luminosity its members to be M31, the Milky Way, M33, the Large Magellanic Cloud, the Small Magellanic Cloud, M32, NGC 205, NGC 6822, NGC 185, IC 1613 and NGC 147. He also identified IC 10 as a possible Local Group member. In the ~70 years since his work, the number of known Local Group members has increased from his initial twelve to thirty-six as of 2003, by way of the discovery of almost two dozen low-luminosity galaxies.^[3]

Component galaxies

Maps

Local group (clickable map)

Milky Way's satellite galaxies (clickable map)

Galactic bodies

Other notable objects

• Smith's Cloud - High velocity cloud, between 32,000 and 49,000 light years from Earth,^[6] and 8000 light years from the disk of the Milky Way Galaxy.^[7]
• HVC 127-41-330 - High velocity cloud, 2.3 million light-years from Earth

Diagram

A diagram of our location in the Local Supercluster. Click to view more detail.

See also

• Groups and clusters of galaxies
• List of nearest galaxies
• List of galaxy clusters
• Local Supercluster
• Andromeda's satellite galaxies
• Milky Way's satellite galaxies

References

External links

• The Local Group of Galaxies, SEDS Messier pages
• A Survey of the Resolved Stellar Content of Nearby Galaxies Currently Forming Stars, Lowell Observatory
• van den Bergh, Sidney (2000). "Updated Information on the Local Group". The Publications of the Astronomical Society of the Pacific 112 (770): 529–536. doi:10.1086/316548. http://adsabs.harvard.edu/abs/2000astro.ph..1040V.  

The Milky Way Location Universe · Virgo Supercluster · Local Group Galactic core Center of the Milky Way Spiral arms Sagittarius-Carina · Scutum-Crux · Norma-Cygnus · Perseus · Orion Satellite galaxies Dwarves Boötes · Canes Venatici · Canis Major · Carina · Draco · Fornax · Leo I · Leo II · Phoenix · Sagittarius Elliptical · Sculptor · Segue 1 · Sextans Spheroidal · Ursa Major I · Ursa Major II · Ursa Minor Other Large Magellanic Cloud · Magellanic Stream · Monoceros Ring · Small Magellanic Cloud · Virgo Stream · Willman 1

Definition from Wiktionary, a free dictionary

English

Noun

Wikipedia has an article on:

Local Group

Wikipedia

Local Group

1. (astronomy) the small cluster of galaxies that contains the Milky Way galaxy; includes Andromeda, Triangulum, the Large Magellanic Cloud, Small Magellanic Cloud and others

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