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Weak Gravitational Lensing
While the presence of any mass bends the path of light passing near it, this effect rarely produces the giant arcs and multiple images associated with strong gravitational lensing. Most lines of sight in the universe are thoroughly in the weak lensing regime, in which the deflection is impossible to detect in a single background source. However, even in these cases, the presence of the foreground mass can be detected, by way of a systematic alignment of background sources around the lensing mass. Weak gravitational lensing is thus an intrinsically statistical measurement, but it provides a way to measure the masses of astronomical objects without requiring assumptions about their composition or dynamical state. Methodology Gravitational lensing acts as a coordinate transformation that distorts the images of background objects (usually galaxies) near a foreground mass. The transformation can be split into two terms, the convergence and shear. The convergence term magnif ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strong Gravitational Lensing
Strong gravitational lensing is a gravitational lensing effect that is strong enough to produce multiple images, arcs, or even Einstein rings. Generally, the strong lensing effect requires the projected lens mass density greater than the '' critical density'', that is \Sigma_\,. For point-like background sources, there will be multiple images; for extended background emissions, there can be arcs or rings. Topologically, multiple image production is governed by the odd number theorem. Strong lensing was predicted by Albert Einstein's general theory of relativity and observationally discovered by Dennis Walsh, Bob Carswell, and Ray Weymann in 1979. They determined that the Twin Quasar Q0957+561A comprises two images of the same object. Observations Most strong gravitational lenses are detected by large-scale galaxy surveys. Galaxy lensing The foreground lens is a galaxy. When the background source is a quasar or unresolved jet, the strong lensed images are usually point-l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Universe
The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. According to this theory, space and time emerged together ago, and the universe has been expanding ever since the Big Bang. While the spatial size of the entire universe is unknown, it is possible to measure the size of the observable universe, which is approximately 93 billion light-years in diameter at the present day. Some of the earliest cosmological models of the universe were developed by ancient Greek and Indian philosophers and were geocentric, placing Earth at the center. Over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System. In developing the law of universal gravitation, Isaac Newton built upon Copernicus's work as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Faint Blue Galaxy
A faint blue galaxy (FBG) is an inconspicuous, often small galaxy with low surface luminosity. In addition to being dim, they show a remarkable preponderance of sparsely scattered, blue stars, but comparatively few red stars, which in most galaxies are by far the most common. They appear as dim, bluish smudges on old photographic plates, with no clear structure or shape, and do not register well on modern electronic cameras, which are more sensitive to red. They are currently interpreted as small dwarf-irregular satellite-galaxies undergoing a burst of star formation. Previously overlooked Although some had been previously photographed as faint smudges in sky surveys, they were first noticed in the 1970s, and posed a problem for the then-current theories of galaxy formation. FBGs tend to found in the peripheries of galaxy clusters, and as remote satellites of large galaxies, and appear to be a now-finished stage of galactic growth. Any galaxy might appear faint because it is smal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ellipse
In mathematics, an ellipse is a plane curve surrounding two focal points, such that for all points on the curve, the sum of the two distances to the focal points is a constant. It generalizes a circle, which is the special type of ellipse in which the two focal points are the same. The elongation of an ellipse is measured by its eccentricity e, a number ranging from e = 0 (the limiting case of a circle) to e = 1 (the limiting case of infinite elongation, no longer an ellipse but a parabola). An ellipse has a simple algebraic solution for its area, but only approximations for its perimeter (also known as circumference), for which integration is required to obtain an exact solution. Analytically, the equation of a standard ellipse centered at the origin with width 2a and height 2b is: : \frac+\frac = 1 . Assuming a \ge b, the foci are (\pm c, 0) for c = \sqrt. The standard parametric equation is: : (x,y) = (a\cos(t),b\sin(t)) \quad \text \quad 0\leq t\leq 2\pi. Ellip ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bell Laboratories
Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by multinational company Nokia. With headquarters located in Murray Hill, New Jersey, the company operates several laboratories in the United States and around the world. Researchers working at Bell Laboratories are credited with the development of radio astronomy, the transistor, the laser, the photovoltaic cell, the charge-coupled device (CCD), information theory, the Unix operating system, and the programming languages B, C, C++, S, SNOBOL, AWK, AMPL, and others. Nine Nobel Prizes have been awarded for work completed at Bell Laboratories. Bell Labs had its origin in the complex corporate organization of the Bell System telephone conglomerate. In the late 19th century, the laboratory began as the Western Electric Engineering Departm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomy And Astrophysics
''Astronomy & Astrophysics'' is a monthly peer-reviewed scientific journal covering theoretical, observational, and instrumental astronomy and astrophysics. The journal is run by a Board of Directors representing 27 sponsoring countries plus a representative of the European Southern Observatory. The journal is published by EDP Sciences and the editor-in-chief is . History Origins ''Astronomy and Astrophysics'' (A&A) was created as an answer to the publishing scenario found in Europe in the 1960s. At that time, multiple journals were being published in several countries around the continent. These journals usually had a limited number of subscribers, and published articles in languages other than English, resulting in a small number of citations compared to American and British journals. Starting in 1963, conversations between astronomers from European countries assessed the need for a common astronomical journal. On 8 April 1968, leading astronomers from Belgium, Denmark, Fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Abell 370
Abell 370 is a galaxy cluster located nearly 5 billion light-years away from the Earth (at redshift ''z'' = 0.375), in the constellation Cetus. Its core is made up of several hundred galaxies. It was catalogued by George Abell, and is the most distant of the clusters he catalogued. In the 1980s astronomers of Toulouse Observatory discovered a gravitational lens in space between Earth and Abell 370. A curious arc had been observed earlier near the cluster, but the astronomers were able to recognize it as this phenomenon. Gravitational lensing Abell 370 appears to include several arcs of light, including the largest ever discovered with 30" long. These arcs or deformations are mirages caused by gravitational lensing of massive and dark objects located between the observer and the distant galaxies. This cluster shows an apparent magnitude of +22. In 2002, astronomers used this lensing effect to discover a galaxy, HCM-6A, 12.8 billion light years away from Earth. At the time it w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Toulouse Observatory
The Toulouse Observatory (french: Observatoire de Toulouse) is located in Toulouse, France and was established in 1733. It was founded by ''l'Académie des Sciences, Inscriptions et Belles-Lettres de Toulouse'' ("Academy of Science, Inscriptions and the Humanities of Toulouse"). It was moved 1841 and again in 1981. In 1987, Genevieve Soucail of the Toulouse Observatory and her collaborators presented data of a blue ring-like structure in Abell 370 and proposed a gravitational lensing interpretation In the 1990s the observatory worked on MEGACAM with several other institutions. People & Directors The observatory was started by Garipuy in the 1730s with support from the Academy of Sciences. Félix Tisserand was a famous director from 1873 to 1878. He published ''Recueil d'exercices sur le calcul infinitesimal'' as well as making several expeditions, including an 1874 trip to Japan. Henri Joseph Anastase Perrotin was Tisserand's assistant astronomer, and they both went to the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stanford University
Stanford University, officially Leland Stanford Junior University, is a Private university, private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is considered among the most prestigious universities in the world. Stanford was founded in 1885 by Leland Stanford, Leland and Jane Stanford in memory of their only child, Leland Stanford Jr., who had died of typhoid fever at age 15 the previous year. Leland Stanford was a List of United States senators from California, U.S. senator and former List of governors of California, governor of California who made his fortune as a Big Four (Central Pacific Railroad), railroad tycoon. The school admitted its first students on October 1, 1891, as a Mixed-sex education, coeducational and non-denominational institution. Stanford University struggled financially after the death of Leland Stanford in 1893 and again after much of the campus was ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
National Optical Astronomy Observatory
The National Optical Astronomy Observatory (NOAO) was the United States national observatory for ground-based nighttime ultraviolet-optical-infrared (OUVIR) astronomy. The National Science Foundation (NSF) funded NOAO to provide forefront astronomical research facilities for US astronomers. Professional astronomers from any country in the world could apply to use the telescopes operated by NOAO under the NSF's "open skies" policy. NOAO was operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the NSF. Its headquarters in Tucson, Arizona were co-located with the headquarters of the National Solar Observatory. The budget for NOAO during the 2017 fiscal year was nearly $23 million. NOAO was founded in 1984 to join the operations of the Kitt Peak National Observatory in the United States with the Cerro Tololo Inter-American Observatory in Chile. On October 1, 2019, NOAO merged its operations with the Gemini Observatory and the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CL0024+17
The cluster CL0024+17 is a cluster of galaxies located in Pisces, and about 4 billion light years distant. Cl 0024+17 is allowing astronomers to probe the distribution of dark matter in space. The blue streaks near the center of the image are the smeared images of very distant galaxies that are not part of the cluster. The distant galaxies appear distorted because their light is being bent and magnified by the powerful gravity of Cl 0024+17, an effect called gravitational lensing 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 .... Because dark matter does not shine or reflect light, it cannot be seen. Astronomers can only detect its influence by how its gravity affects light. By mapping the distorted light created by gravitational lensing, astronomers can trace how dark matter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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