Hodge, Paul Department of Astronomy, University of Washington, Seattle, Washington.
Turner, Edwin L. Princeton University Observatory, Princeton, New Jersey.
Turner, Joyce B. Princeton University Observatory, Princeton, New Jersey.
Khochfar, Sadegh Max-Planck-Institute for Extraterrestrial Physics, Garching, Germany.
Silk, Joseph Department of Physics, University of Oxford, Oxford, United Kingdom.
- Form and size
- Exotic galaxy types
- Internal motions
- Active nuclei
- Links to Primary Literature
- Additional Readings
One of the large self-gravitating aggregates of stars, gas, and dust that contain a large amount of the visible baryonic matter in the universe. Typical large galaxies have symmetric and regular forms, are about 50,000 light-years (3 × 1017 mi or 5 × 1017 km) in diameter, and are roughly 3 × 1010 times more luminous than the Sun. The stars and other material within a galaxy move through it, often in regular rotation, with periods of a few hundred million years. The characteristic mass associated with a large galaxy is a few times 1012 solar masses. (The solar mass is 4.4 × 1030 lb or 2 × 1030 kg.) Galaxies often occur in groups or clusters containing from a few to many thousands of individual galaxies and ranging in size from a few hundred thousands to tens of millions of light-years. The nearest galaxy to the Milky Way Galaxy, the Sagittarius Dwarf Galaxy, is about 80,000 light-years (4 × 1017 mi or 6 × 1017 km) away; the farthest, more than 1 × 1010 light-years (6 × 1022 mi or 1 × 1023 km). Galaxies are the landmarks by which cosmologists survey the large-scale structure of the universe. See also: Baryon
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