Local Group (astronomy)

Local Group in astronomy, loose cluster of at least 35 nearby galaxies , including our own Milky Way galaxy, the Andromeda Galaxy , and the Magellanic Clouds . The Local Group is spread over an ellipsoidal region of space with a major axis of approximately 3 million light-years. The Milky Way galaxy, near one end of the major axis, and the Andromeda Galaxy, near the other end, are the largest members of the group. Some of the galaxies in the group have been detected only by their infrared radiation ; a dusty region in space obscures their visible light. There may be other galaxies in the Local Group that are as yet undetected. As shown by the work of G. de Vaucouleurs, the Local Group is part of a supercluster containing at least 50 separate clusters, each having from a few dozen to as many as a thousand galaxies. These groups appear to be concentrated in a plane, which indicates that the supercluster is rotating. Its center lies approximately 50 million light-years away in the direction of the constellation Virgo.

Local Group The group of galaxies about 3 million l.y. in diameter which contains our Galaxy. There are 36 confirmed members of the Local Group (see Table 7, Appendix). The nearest other prominent galaxies (Sculptor and M81 groups) are considerably farther away, about 10 million l.y. The total mass of the Local Group is estimated at about 2 × 10¹² solar masses. The brightest members are the three spirals: the Andromeda Galaxy, our Galaxy, and M33. A few dwarf spheroidal galaxy members may remain undiscovered.