Local Group

The Local Group of galaxies. The Milky Way and Andromeda are the most massive galaxies by far. (Click to enlarge)

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 covers a diameter of 10 Mly (3.1 Mpc) (about 10^23 meters) and has a binary (dumbbell)^[1] distribution. The group itself is a part of the larger Virgo Supercluster, which in turn may be a part of the Laniakea Supercluster.

The two most massive members of the group are the Milky Way and Andromeda galaxies.^[2] These two spiral galaxies have each a system of satellite galaxies.

• Milky Way's satellite galaxies system comprises 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 I Dwarf and Ursa Major II Dwarf, plus several additional ultra-faint dwarf spheroidal galaxies.^[3]
• The Andromeda Galaxy's satellite system consists of Messier 32 (M32), Messier 110 (M110), NGC 147, NGC 185, Andromeda I (And I), And II, And III, And IV, And V, Pegasus dSph (aka And VI), Cassiopeia Dwarf (aka And VII), And VIII, And IX, And X, And XI, And XIX, And XXI and And XXII, plus several additional ultra-faint dwarf spheroidal galaxies.
• The Triangulum Galaxy, the third largest and only unbarred spiral galaxy in the Local Group, may or may not be a companion to the Andromeda Galaxy. Pisces Dwarf is equidistant from the Andromeda Galaxy and the Triangulum Galaxy, so it may be a satellite of either.^[4]
• The membership of NGC 3109, with its companions Sextans A and the Antlia Dwarf, is uncertain due to extreme distances from the center of the Local Group.
• The other members of the group are gravitationally secluded from these large subgroups: IC 10, IC 1613, 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 1936 book The Realm of the Nebulae.^[5] There, he described it as "a typical small group of nebulae which is isolated in the general field". He 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 Local Group member. By 2003, the number of known Local Group members has increased from his initial 12 to 36 by way of the discovery of almost two dozen low-luminosity galaxies.^[6]

Component galaxies

Map

Local Group (clickable map)

List of galactic bodies

Other notable objects

• Smith's Cloud, a high-velocity cloud, between 32,000 and 49,000 light years from Earth,^[9] and 8,000 light years from the disk of the Milky Way Galaxy^[10]
• HVC 127-41-330, a high-velocity cloud, 2.3 million light-years from Earth
• Monoceros Ring, a ring of stars around the Milky Way which is proposed to consist of a stellar stream torn from the Canis Major Dwarf Galaxy

Diagram

A diagram of our location in the observable universe. (Click here for smaller image.)

See also

• Galaxy cluster
• List of nearest galaxies
• List of galaxy clusters
• IC 342/Maffei Group, the group of galaxies nearest to the Local Group.
• Local Supercluster
• List of Andromeda's satellite galaxies
• List of Milky Way's satellite galaxies

References

External links

Wikimedia Commons has media related to Local Group.

• 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. arXiv:astro-ph/0001040. Bibcode:2000PASP..112..529V. doi:10.1086/316548. 

The Milky Way Location Milky Way → Milky Way subgroup → Local Group → 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 Boötes I Boötes III Canes Venatici I Canes Venatici II Canis Major Carina Draco Fornax Hercules Leo I Leo II Leo IV Leo V Phoenix Pisces I Pisces II Sculptor Sextans Triangulum II Ursa Major I Ursa Major II Ursa Minor Other Monoceros Ring Virgo Stream Koposov I Koposov II Segue 3 Willman 1 Related Andromeda–Milky Way collision Astronomy portal

Andromeda Galaxy Location Andromeda Galaxy→Andromeda subgroup → Local Group → Virgo Supercluster → Laniakea Supercluster → Observable universe → Universe Each  → may be read as "within" or "part of". Satellite galaxies M32 M110 NGC 185 NGC 147 Andromeda I Andromeda II Andromeda III Andromeda IV* Andromeda V Andromeda VI Andromeda VII Andromeda VIII Andromeda IX Andromeda X Andromeda XI Andromeda XII Andromeda XIII Andromeda XIV Andromeda XV Andromeda XVI Andromeda XVII Andromeda XVIII Andromeda XIX Andromeda XX Andromeda XXI Andromeda XXII Andromeda XXIII Andromeda XXIV Andromeda XXV Andromeda XXVI Andromeda XXVII Andromeda XXVIII Andromeda XXIX Triangulum Galaxy* *It is uncertain whether the Triangulum Galaxy is a companion galaxy of the Andromeda Galaxy Other Andromeda–Milky Way collision S Andromedae Mayall II NGC 206 AE Andromedae

Triangulum Galaxy Location Triangulum Galaxy→ Triangulum subgroup→ Local Group→ Virgo Supercluster→ Laniakea Supercluster→ Observable universe→ Universe Each → may be read as "within" or "part of". H II regions NGC 595 NGC 604 Suspected satellite galaxies Pisces Dwarf Andromeda II Other Triangulum Galaxy in fiction

Earth's location in the Universe Earth → Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Virgo Supercluster → Laniakea Supercluster → Observable universe → Universe Each arrow (→) may be read as "within" or "part of". Astronomy portal - Cosmology portal