Wednesday, December 10, 2008

The Local Group

The Local Group is the group of galaxies that includes the Milky Way, the galaxy in which our solar system is found. The group comprises over 35 galaxies, with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy. The Local Group has a 10 million light-year diameter and have a binary (dumbbell) shape. The group is estimated to have a total mass of (1.29 ± 0.14)×1012M. The group itself is one of many within the Virgo Supercluster. The two most massive members of the group are the Milky Way and the Andromeda Galaxy. These two barred spirals each have a system of nearby 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 third-largest galaxy of the Local Group is the Triangulum Spiral M33.
The Local Group was first identified by Edwin Hubble in 1935, and later mentioned in the chapter VI of his book The Realm of Nebulae published in 1936.