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Local Group

Group of galaxies that includes the Milky Way / From Wikipedia, the free encyclopedia

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The Local Group is the galaxy group that includes the Milky Way. It has a total diameter of roughly 3 megaparsecs (10 million light-years; 9×1019 kilometres),[1] and a total mass of the order of 2×1012 solar masses (4×1042 kg).[2] It consists of two collections 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 collections are separated by about 800 kiloparsecs (3×10^6 ly; 2×1019 km) and are moving toward one another with a velocity of 123 km/s.[3] The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster. The exact number of galaxies in the Local Group is unknown as some are occluded by the Milky Way; however, at least 80 members are known, most of which are dwarf galaxies.

Quick facts: Local Group, Observation data (Epoch J2000), ...
Local Group
Local Group of galaxies, including the massive members Messier 31 (Andromeda Galaxy) and Milky Way, as well as other nearby galaxies.
Local Group of galaxies, including the massive members Messier 31 (Andromeda Galaxy) and Milky Way, as well as other nearby galaxies.
Observation data (Epoch J2000)
Parent structureVirgo Supercluster
See also: Galaxy group, Galaxy cluster, List of galaxy groups and clusters
Distribution of the iron content (in logarithmic scale) in four neighbouring dwarf galaxies of the Milky Way

The two largest members, the Andromeda and the Milky Way galaxies, are both spiral galaxies with masses of about 1012 solar masses each. Each has its own system of satellite galaxies:

Visual size comparison of the six largest Local Group galaxies, with details

The Triangulum Galaxy (M33) is the third-largest member of the Local Group, with a mass of approximately 5×1010 M (1×1041 kg), and is the third spiral galaxy.[6] It is unclear whether the Triangulum Galaxy is a companion of the Andromeda Galaxy; the two galaxies are 750,000 light years apart,[7] and 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.[8]

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.[3] 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.[9]

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