Shipman, Harry L. Department of Physics, University of Delaware, Newark, Delaware.
Last reviewed:July 2021
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- Strong lensing and weak lensing
- Discovery of lenses
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A massive body producing distorted, magnified, or multiple images of more distant objects when its gravitational fields bend the paths of light rays. Examples of foreground bodies that can act as gravitational lenses of background objects include highly massive galaxy clusters or individual galaxies. When stars or planets act as gravitational lenses, the effect is known as gravitational microlensing. Background objects can be galaxy clusters or standalone galaxies, oftentimes luminous quasars (Fig. 1). In the case of microlensing, the background objects can be anything that emits or reflects electromagnetic radiation, including stars, brown dwarfs, exoplanets, white dwarfs, neutron stars, and black holes (that is, if the black hole's immediate environment is emitting radiation, for instance from an accretion disk). Astronomers use gravitational lenses to study properties of galaxies and quasars, as well as provide information on the universe and its contents, including matter, dark matter, and dark energy. Microlensing is useful for many astrophysical investigations, including the discovery of distant exoplanets that would otherwise be difficult or impossible to detect. See also: Astronomy; Brown dwarf; Dark energy; Dark matter; Exoplanet; Galaxy; Matter; Quasar; Star; Universe
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