Local Group

The Local Group is the galaxy group that includes the Milky Way. It has a total diameter of roughly 3 Mpc (or 10 Mly ≈ 1023 m), and a total mass of the order of 2×1012 solar masses (4×1042 kg).It consists of two clusters of galaxies in a 'dumbbell' shape, the Milky Way and its satellites on one hand, and the Andromeda Galaxy and its satellites on the other. The two clusters are separated by about 0.8 Mpc and move towards one another with a velocity of 123 km/h. 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 (due to its partial occlusion by the Milky Way) but known to exceed 54, most of them beingdwarf galaxies.at about 125% of the mass of the Milky Way.Diameter: 220 kly, mass: (1.15±0.35)×1012 M☉, number of stars: ca. 1012.Diameter: 175±25 kly,mass: (1.3±0.3)×1012 M☉,number of stars: (2.5±1.5)×1011.Diameter: 60 kly, mass: 5×1010 M☉, number of stars: 4×1010.*It is uncertain whether it is a companion galaxy of the Andromeda Galaxy The Local Group is the galaxy group that includes the Milky Way. It has a total diameter of roughly 3 Mpc (or 10 Mly ≈ 1023 m), and a total mass of the order of 2×1012 solar masses (4×1042 kg).It consists of two clusters of galaxies in a 'dumbbell' shape, the Milky Way and its satellites on one hand, and the Andromeda Galaxy and its satellites on the other. The two clusters are separated by about 0.8 Mpc and move towards one another with a velocity of 123 km/h. 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 (due to its partial occlusion by the Milky Way) but known to exceed 54, most of them beingdwarf galaxies. The two largest members, the Andromeda Galaxy and the Milky Way, are both spiral galaxies with masses of about 1012 solar masses each, and each have their own system of satellite galaxies: The Triangulum Galaxy is the third largest member of the Local Group, at about 5×1010 M☉, and the third spiral galaxy. It may or may not be a companion to the Andromeda Galaxy. 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. 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 Local Group. By 2003, the number of known Local Group members had increased from his initial 12 to 36.