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Chang–Refsdal Lens
A Chang–Refsdal lens is a point-mass gravitational lens (e.g. black hole) perturbed by constant external shear. The name derives from Kyongae Chang and who in 1979 published a paper in NATURE 282, 561. "Flux Variations of QSO Q0957+561 A,B and image splitting by stars Near the Light Path." The paper illustrated that stars could affect image brightness.
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Gravitational Lens
A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer. This effect is known as gravitational lensing, and the amount of bending is one of the predictions of Albert Einstein's general theory of relativity. Treating light as corpuscles travelling at the speed of light, Newtonian physics also predicts the bending of light, but only half of that predicted by general relativity. Although Einstein made unpublished calculations on the subject in 1912, Orest Khvolson (1924) and Frantisek Link (1936) are generally credited with being the first to discuss the effect in print. However, this effect is more commonly associated with Einstein, who published an article on the subject in 1936. Fritz Zwicky posited in 1937 that the effect could allow galaxy clusters to act as gravitational lenses. It was not until 1979 that this ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Black Hole
A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary (topology), boundary of no escape is called the event horizon. Although it has a great effect on the fate and circumstances of an object crossing it, it has no locally detectable features according to general relativity. In many ways, a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with thermal radiation, the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly. Obje ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kyongae Chang
Kyongae Chang (, born September 5, 1946) is a South Korean astrophysicist. She is best known for her work on gravitational lensing, including the Chang-Refsdal lens. Chang was born in Seoul. She worked as a research associate on astrometric binaries with Professors van de Kamp and Heintz at Sproul Observatory from 1969 till 1971. From 1975 until 1980 she worked on a Dr. rer. nat. at Hamburg University, graduating with her work on the Chang-Refsdal lens. The main result was published in ''Nature'' in 1979 immediately after the discovery of the first gravitational lens. She returned to Korea in 1985 and became a professor at Cheongju University. References External linksPartial list of publicationsat ScientificCommonsKyongae Changat the IAU The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical resear ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sjur Refsdal
Sjur Refsdal (30 December 1935 – 29 January 2009) was a Norwegian astrophysicist, born in Oslo. He is best known for his pioneer work on gravitational lensing, including the Chang-Refsdal lens. Biography In 1970 he earned a doctorate at the Institute of Theoretical Astrophysics, University of Oslo. Later that year he became professor in astrophysics at the Hamburg Observatory in Germany, and remained in that position until he retired in 2001. In 1964 and 1966 he published a series of articles on the effects and possible applications of gravitational lenses. He is particularly known for the "Refsdal Method", which describes how one may estimate the expansion rate of the Universe (Hubble constant) using the measured time-delay and lens properties of a gravitationally lensed Supernova (SN). This method was applied for the first time in 2018, with the homonymous SN Refsdal. He later started work on stellar evolution, but returned to gravitational lensing shortly before the fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quasar
A quasar is an extremely Luminosity, luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Gas in the disc falling towards the black hole heats up because of friction and releases energy in the form of electromagnetic radiation. The radiant energy of quasars is enormous; the most powerful quasars have luminosity, luminosities thousands of times greater than that of a galaxy such as the Milky Way. Usually, quasars are categorized as a subclass of the more general category of AGN. The redshifts of quasars are of Expansion of the universe, cosmological origin. The term originated as a Contraction (grammar), contraction of "quasi-stellar ''[star-like]'' radio source"—because quasars were first identified during the 1950s as sour ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microlensing
Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit much light (stars) or large objects that block background light (clouds of gas and dust). These objects make up only a minor portion of the mass of a galaxy. Microlensing allows the study of objects that emit little or no light. When a distant star or quasar gets sufficiently aligned with a massive compact foreground object, the bending of light due to its gravitational field, as discussed by Albert Einstein in 1915, leads to two distorted images (generally unresolved), resulting in an observable magnification. The time-scale of the transient brightening depends on the mass of the foreground object as well as on the relative proper motion between the background 'source' and the foreground 'lens' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MACHO
Machismo (; ; ; ) is the sense of being " manly" and self-reliant, a concept associated with "a strong sense of masculine pride: an exaggerated masculinity". Machismo is a term originating in the early 1930s and 1940s best defined as having pride in one’s masculinity. It is associated with "a man's responsibility to provide for, protect, and defend his family". Machismo is strongly and consistently associated with dominance, aggression, exhibition, and nurturance. The correlation to machismo is found to be deeply rooted in family dynamics and culture. The word has a long history both in Spain and Portugal, including the Spanish and Portuguese languages. in Portuguese and Spanish is a strictly masculine term, derived from from the Latin ''mascŭlus'', which means "male". It was originally associated with the ideal societal role men were expected to play in their communities, most particularly Iberian language-speaking societies and countries. In addition, due to Mexico ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quasar
A quasar is an extremely Luminosity, luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Gas in the disc falling towards the black hole heats up because of friction and releases energy in the form of electromagnetic radiation. The radiant energy of quasars is enormous; the most powerful quasars have luminosity, luminosities thousands of times greater than that of a galaxy such as the Milky Way. Usually, quasars are categorized as a subclass of the more general category of AGN. The redshifts of quasars are of Expansion of the universe, cosmological origin. The term originated as a Contraction (grammar), contraction of "quasi-stellar ''[star-like]'' radio source"—because quasars were first identified during the 1950s as sour ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
