Fan, Xiaohui Steward Observatory, The University of Arizona, Tucson, Arizona.
- Nature of quasar redshifts
- General characteristics
- 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. The name quasar is a contraction of the term quasi-stellar object (QSO), or quasi-stellar radio source, which was originally applied to these objects for their stellar photographic appearance. The objects appear starlike because their angular diameters are less than about 1 second of arc, which is the resolution limit of ground-based optical telescopes imposed by atmospheric effects. However, high-resolution images using space telescopes and ground-based telescopes with adaptive optics have revealed that quasars reside in the centers of active galaxies. They are the most luminous members of a larger family of objects that are generally referred to as active galactic nuclei (AGNs). They often outshine their host galaxies by a factor of 100–1000. They are among the most luminous and energetic sources in the universe. Because of their high luminosity, they can be detected at great distances and therefore are also among the most distant objects ever observed. Astronomers generally believe that the accretion of hot gas into supermassive black holes at galactic centers provides the energy that powers quasars. Quasars are useful probes of cosmology, the formation of black holes, and the evolution of galaxies in the universe. See also: Adaptive optics; Black hole; Cosmology; Galaxy, external; Telescope; Universe
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