Galaxy - Galaxy NGC 4414, a typical spiral galaxy in the...

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Galaxy NGC 4414 , a typical spiral galaxy in the constellation Coma Berenices , is about 55,000 light- years in diameter and approximately 60 million light-years away from Earth. A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants , an interstellar medium of gas and dust , and an important but poorly understood component tentatively dubbed dark matter . [1] [2] The word galaxy is derived from the Greek galaxias (γαλαξίας), literally "milky", a reference to the Milky Way galaxy. Examples of galaxies range from dwarfs with as few as ten million (10 7 ) stars [3] to giants with a hundred trillion (10 14 ) stars, [4] each orbiting their galaxy's own center of mass . Galaxies contain varying amounts of star systems , star clusters and types of interstellar clouds . In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays . Dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests that
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