Galaxy

:This article is about celestial bodies. For alternate meanings, see galaxy (disambiguation).

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A galaxy is a large gravitationally bound system of stars, interstellar gas and dust, plasma and unseen dark matter. Typical galaxies contain 10 million to one trillion (107 to 1012) or more stars, all orbiting a common center of gravity. In addition to single stars and a tenuous interstellar medium, most galaxies contain a large number of multiple star systems and star clusters as well as various types of nebulae. Most galaxies are several thousand to several hundred thousand light years in diameter and are usually separated from one another by distances on the order of millions of light years.

Related Topics:
Gravitationally bound - Stars - Interstellar gas and dust - Plasma - Dark matter - 10⁷ - Center of gravity - Multiple star systems - Star clusters - Nebulae - Light years

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Although so called dark matter and dark energy appear to account for well over 90% of the mass of most galaxies, the nature of these unseen components is not well understood. There is some evidence that supermassive black holes may exist at the center of many, if not all, galaxies.

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Intergalactic space, the space between galaxies, is a tenuous plasma with an average density of less than one atom per cubic meter of gas or dust. There are probably more than 1011 galaxies in the visible universe.

Related Topics:
Intergalactic space - Plasma - 10¹¹ - Universe

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