Sinonimi: extragalactic nebula
ETYM French galaxie, Latin galaxias, from Greek gala milk; akin to Latin lac. Related to Lacteal.
1. A splendid assemblage (especially of famous people).
2. (Astronomy) A collection of star systems; any of the billions of systems each having many stars and nebulae and dust; SYN. extragalactic nebula.
Milky Way; island universe, especially one to which solar system and all visible stars belong; collection of brilliant persons.
Congregation of millions or billions of stars, held together by gravity. Spiral galaxies, such as the Milky Way, are flattened in shape, with a central bulge of old stars surrounded by a disc of younger stars, arranged in spiral arms like a Catherine wheel. Barred spirals are spiral galaxies that have a straight bar of stars across their center, from the ends of which the spiral arms emerge. The arms of spiral galaxies contain gas and dust from which new stars are still forming. Elliptical galaxies contain old stars and very little gas. They include the most massive galaxies known, containing a trillion stars. At least some elliptical galaxies are thought to be formed by mergers between spiral galaxies. There are also irregular galaxies. Most galaxies occur in clusters, containing anything from a few to thousands of members.
Our own galaxy, the Milky Way, is about 100,000 light-years in diameter, and contains at least 100 billion stars. It is a member of a small cluster, the Local Group. The Sun lies in one of its spiral arms, about 25,000 light-years from the center.
In 1995, two galaxies were discovered obscured by galactic dust at the edge of the Milky Way. One, named MB1, is a spiral galaxy 17,000 light-years across; the other, MB2, is an irregular-shaped dwarf galaxy about 4,000 light-years across.