Local Group


The Local Group is the galaxy group that includes the Milky Way.
It has a total diameter of roughly, and a total mass of the order of.
It consists of two clusters of galaxies in a "dumbbell" shape: the Milky Way and its satellites form one lobe, and the Andromeda Galaxy and its satellites constitute the other. The two clusters are separated by about and move towards one another with a velocity of. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster.
The total number of galaxies in the Local Group is unknown as some are occluded by the Milky Way; however, at least 80 such objects are known.
The two largest members, the Andromeda Galaxy and the Milky Way, are both spiral galaxies with masses of about solar masses each, and each have their own system of satellite galaxies:
The Triangulum Galaxy is the third-largest member of the Local Group, with a mass of approximately, and is the third spiral galaxy. It is unclear whether the Triangulum Galaxy is a companion of the Andromeda Galaxy, although the two galaxies experienced a close passage 2–4 billion years ago which triggered star formation across Andromeda's disk. The Pisces Dwarf Galaxy is equidistant from the Andromeda Galaxy and the Triangulum Galaxy, so it may be a satellite of either.
The membership of NGC 3109, with its companions Sextans A and the Antlia Dwarf Galaxy, is uncertain due to extreme distances from the center of the Local Group.
The other members of the group are likely gravitationally secluded from these large subgroups: IC 10, IC 1613, Phoenix Dwarf Galaxy, Leo A, Tucana Dwarf Galaxy, Cetus Dwarf Galaxy, Pegasus Dwarf Irregular Galaxy, Wolf–Lundmark–Melotte, Aquarius Dwarf Galaxy, and Sagittarius Dwarf Irregular Galaxy.

History

The term "The Local Group" was introduced by Edwin Hubble in Chapter VI of his 1936 book The Realm of the Nebulae. 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 the Local Group.

Component galaxies

Map

List of galactic bodies

Other objects