Galaxy (Encyclopedia of Science)
A galaxy is a large collection of stars, glowing nebulae (clouds), gas, and dust bound together by gravity. Many scientists now believe that a black hole, the remains of a massive star, lies at the center of many galaxies. Galaxies are as plentiful in the universe as grains of sand on a beach. The galaxy that contains our solar system is called the Milky Way. The Milky Way is part of a cluster of some 30 galaxies known as the Local Group, and the Local Group is part of a local supercluster that includes many clusters.
Although astronomers are not yet sure how galaxies formed and evolved, the process must have occurred quickly very early in the history of the universe. The age of the oldest galaxies appears to be about the same age as the universe, which is...
(The entire section is 1348 words.)
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