Local Group

The Local Group is the set of forty galaxies belongs to ours. Its diameter is about 3 million parsecs (about 10 million light years ). The Local Group appears to be a typical representative of groups of galaxies that are in the universe. It has nearly all common types of galaxies , with the exception of giant elliptical galaxies that are never present in such small structures.

The designation "local group" is due to the American astronomer Edwin Hubble , who used it in the course of the 1930s in his book The Realm of Nebulae. It had identified 12 galaxies at the time, including 3 that it considered dubious. Two of them have in fact proved not to belong to the Local Group. Walter Baade increase the number of galaxies in the Local Group in 1963 to 18, one of which will be subsequently excluded. Between 1963 and 2000, the discovery of several dwarf galaxies reduced the number to 35, with a rate of almost constant discovery of four galaxies per decade. The exact number of galaxies in the Local Group is uncertain because of difficulties in detecting the fainter members, and uncertainty about the actual physical expansion of the Local Group.

Features

The two principal members of this group are the Andromeda Galaxy (M31) and our galaxy , each with its own galaxy satellites.

Around the Milky Way, orbiting the two Magellanic clouds and galaxies of Canis Major , the Sagittarius , the Little Bear , the Dragon , the hull of the Sextant , the sculptor , the Furnace of Leo I , the Lion II and Toucan. The Canis Major dwarf galaxy is the nearest galaxy to ours, about 25,000 light years away.

The system includes Andromeda M32 , M110 , NGC 147 , NGC 185 , Andromeda I , Andromeda II , III Andromeda and Andromeda IV. The Triangulum Galaxy (M33), the third largest galaxy in the Local Group, is or is not a companion of the Andromeda galaxy but probably has Pisces dwarf galaxy as a satellite.

Other members of the Local Group are gravitationally independent of these large subgroups.

Members

The following lists the members of the local group, ordered by increasing distance from the Earth :

Localization in the universe

The Local Group as a whole regarded as typical of a few tens of galaxies. This set interacts weakly with its neighbors, such as IC 342/Maffei Group , the Sculptor filament or the Cloud of Hunting Dogs. All are located on the outskirts of a galaxy cluster relatively solid, called the Virgo cluster (sometimes, though rarely called Amas local). The Virgo cluster is itself the center of a larger structure called the Virgo Supercluster (or local supercluster). Membership in the strict sense of the Local Group to the Virgo cluster is ambiguous because of its distance from it. The Local Group is shifting away from the Virgo cluster (due to the expansion of the Universe ), but it is not excluded that the mass of the Local Supercluster as a whole and the latter near futures are sufficient to retain the Local Group and to drop him.

See also

Related articles

• galaxy classification
• galaxy
• spiral galaxy
• elliptical galaxy
• irregular galaxy
• dwarf galaxy
• Hubble sequence

External Links

• (In) The Local Group of Galaxies - Page of the local group of SEDS

• Astronomy portal

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