Fan, Xiaohui Steward Observatory, The University of Arizona, Tucson, Arizona.
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- General characteristics
- Very small angular size
- High luminosity
- Broadband continuum emission
- Strong and broad emission lines
- Surveys of quasars
- Quasar model and energy source
- Quasars and cosmology
- Links to Primary Literature
- Additional Readings
An astronomical object that appears starlike on ground-based images but possesses many other characteristics, such as a large redshift, that prove it is not a star. Quasars are the most luminous members of a larger family of objects referred to as active galactic nuclei (AGNs). Found at the centers of galaxies, quasars often outshine their galactic host by a factor of 100–1000, making them among the most luminous and energetic sources in the universe. Because of their high luminosity, quasars can be detected at great distances, and are therefore also among the most distant objects ever observed. Astronomers widely believe that the accretion of hot gas into supermassive black holes at galactic centers provides the energy that powers quasars (Fig. 1). Quasars are useful probes of cosmology, the formation of black holes, and the evolution of galaxies in the universe. See also: Black hole; Cosmology; Galaxy; Supermassive black hole; Universe
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