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Encyclopedia > Gravitational lens
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edit General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915/16. ... Image File history File links Download high resolution version (1024x768, 7 KB) Description: Gravitational light deflection at a neutron star Source: Gallery of Tempolimit Lichtgeschwindigkeit Date: 09. ... General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915/16. ... // Creation of General Relativity Early investigations The development of general relativity began in 1907 with the publication of an article by Albert Einstein on acceleration under special relativity. ... Notational point: General relativity articles using tensors will use the abstract index notation . ... // Books Popular Geroch, Robert (1981). ... Tests of Einsteins general theory of relativity did not provide an experimental foundation for the theory until well after it was introduced in 1915. ... A black hole is an object predicted by general relativity,[1] with a gravitational field so powerful that even electromagnetic radiation (including light itself) cannot escape its pull. ... This article or section is in need of attention from an expert on the subject. ... In relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ... This article or section is in need of attention from an expert on the subject. ... // In general relativity, an exact solution is a Lorentzian manifold equipped with certain tensor fields which are taken to model states of ordinary matter, such as a fluid, or classical nongravitational fields such as the electromagnetic field. ... The Friedmann-Lemaître-Robertson-Walker (FLRW) metric describes a homogeneous, isotropic expanding/contracting universe. ... In physics, a gravitational wave is a fluctuation in the curvature of spacetime which propagates as a wave, traveling outward from a moving object or system of objects. ... In general relativity, the Kerr metric (or Kerr vacuum) describes the geometry of spacetime around a rotating massive body, such as a rotating black hole. ... This article or section does not cite its references or sources. ... It has been suggested that Deriving the Schwarzschild solution be merged into this article or section. ... This article or section is in need of attention from an expert on the subject. ... Albert Einstein ( ) (March 14, 1879 – April 18, 1955) was a German-born theoretical physicist who is widely considered one of the greatest physicists of all time. ... Stephen William Hawking, CH, CBE, FRS (born 8 January 1942) is an English theoretical physicist. ... Spiral Galaxy ESO 269-57 Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature, and chemical composition) of celestial objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ... Gravity redirects here. ... Cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ... The special theory of relativity was proposed in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. Some three centuries earlier, Galileos principle of relativity had stated that all uniform motion was relative, and that there was no absolute and well-defined state of rest... In differential geometry, Riemannian geometry is the study of smooth manifolds with Riemannian metrics, i. ...

A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is "bent" around a massive object (such as a massive galaxy) between the source object and the observer. The process is known as gravitational lensing, and is one of the predictions of Albert Einstein's general relativity theory. It is sometimes known as the Einstein effect, although that is not the only meaning attributed to that term. Artists impression of quasar GB1508 A quasar (contraction of QUASi-stellAR radio source) is an astronomical source of electromagnetic energy, including light, which shows a very high redshift. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light-years in diameter and approximately 60 million light-years distant. ... Tests of Einsteins general theory of relativity did not provide an experimental foundation for the theory until well after it was introduced in 1915. ... Albert Einstein ( ) (March 14, 1879 – April 18, 1955) was a German-born theoretical physicist who is widely considered one of the greatest physicists of all time. ... General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915/16. ... The word theory has a number of distinct meanings in different fields of knowledge, depending on their methodologies and the context of discussion. ... The Einstein effect may mean: Gravitational redshift (Einstein shift) Gravitational lensing There are also: The Bose-Einstein effect The Einstein-de Haas effect Category: ...

Contents

Description

Bending light around a massive object from a distant source. The orange arrows show the apparent position of the background source. The white arrows show the path of the light from the true position of the source.
Bending light around a massive object from a distant source. The orange arrows show the apparent position of the background source. The white arrows show the path of the light from the true position of the source.

In a gravitational lens, the gravity from the massive object bends light like a lens. As a result, the path of the light from the source is curved, distorting its image, and the apparent location of the source may be different from its actual position. In addition, the observer may see multiple images of a single source. If the source, massive object, and the observer lie on a straight line, the source will appear as a ring behind the massive object. This phenomenon was first mentioned in 1924 by the St. Petersburg physicist Orest Chwolson [1], and quantified by Einstein in 1936. It is usually referred to in the literature as an Einstein ring, since Chwolson did not concern himself with the flux or radius of the ring image. More commonly, the massive galaxy is off-center, creating a number of images according to the relative positions of the source, lens, and observer, and the shape of the gravitational well of the lensing galaxy. Description: Illustration for gravitational lens. ... Description: Illustration for gravitational lens. ... Gravity is a force of attraction that acts between bodies that have mass. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength[1]. The elementary particle that defines light is the photon. ... A lens. ... Saint Petersburg (Russian: Санкт-Петербу́рг, English transliteration: Sankt-Peterburg), colloquially known as Питер (transliterated Piter), formerly known as Leningrad (Ленингра́д, 1924–1991) and... Einstein redirects here. ... 1936 (MCMXXXVI) was a leap year starting on Wednesday (link will take you to calendar). ... A beautiful example of an Einstein ring is the radio source B1938+666 discovered with the UK radiotelescope. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light-years in diameter and approximately 60 million light-years distant. ...


There are three classes of gravitational lensing:

  1. Strong lensing: where there are easily visible distortions such as the formation of Einstein rings, arcs, and multiple images.
  2. Weak lensing: where the distortions of background objects are much smaller and can only be detected by analysing large numbers of objects to find distortions of only a few percent. The lensing shows up statistically as a preferred stretching of the background objects perpendicular to the direction to the center of the lens.
  3. Microlensing: where no distortion in shape can be seen but the amount of light received from a background object changes in time. The background source and the lens may be stars in the Milky Way in one typical case, and stars in a remote galaxy and an even more distant quasar in another case.

The effect is small, such that (in the case of strong lensing) a galaxy having a mass of over 100 billion solar masses will produce multiple images separated by only a few arcseconds. Galaxy clusters can produce separations of several arcminutes. In both cases the galaxies and sources are quite distant, many hundreds of megaparsecs away from our Galaxy. A beautiful example of an Einstein ring is the radio source B1938+666 discovered with the UK radiotelescope. ... Gravitational microlensing is an astronomical technique used to find planet-sized bodies indirectly by means of their gravitational interaction with light. ... The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Galaxia Kuklos; or simply the Galaxy) is a barred spiral galaxy in the Local Group, and has special significance to humanity as the location of the solar system, which is located near the Orion... Artists impression of quasar GB1508 A quasar (contraction of QUASi-stellAR radio source) is an astronomical source of electromagnetic energy, including light, which shows a very high redshift. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... A second of arc or arcsecond is a unit of angular measurement which comprises one-sixtieth of an arcminute, or 1/3600 of a degree of arc or 1/1296000 ≈ 7. ... Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ... The megaparsec (abbreviated Mpc) is a unit of distance used in astronomy, equal to one million parsecs. ...


Gravitational lenses act equally on all kinds of electromagnetic radiation, not just visible light. Weak lensing effects are being studied for the cosmic microwave background as well as galaxy surveys. Strong lenses have been observed in radio and x-ray regimes as well. If a strong lens produces multiple images, there will be a relative time delay between two paths: that is, in one image the lensed object will be observed before the other image. Electromagnetic radiation can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... WMAP image of the CMB anisotropy,Cosmic microwave background radiation(June 2003) The cosmic microwave background radiation (CMB) is a form of electromagnetic radiation that fills the whole of the universe. ... A galaxy survey is a survey of galaxies in two or three dimensions. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...


Simulation

Simulated gravitional lensing (black hole going past a background galaxy).

To the right is a simulation of gravitational lensing caused by a Schwarzschild black hole passing in front of a background galaxy. A secondary image of the galaxy can be seen within the black hole's Einstein ring on the side opposite the galaxy. The secondary image grows (remaining within the Einstein ring) as the primary image approaches the black hole. The surface brightness of the two images remains constant, but their angular sizes vary, hence producing an amplification of the galaxy luminosity as seen by a distant observer. Maximum amplification occurs when the galaxy (or in this case a bright part of it) is exactly behind the black hole. Image File history File links BlackHole_Lensing_2. ... Image File history File links BlackHole_Lensing_2. ... A Schwarzschild black hole or static black hole is a black hole fully defined by its only parameter, the mass M. In general black holes could have in addition angular momentum (rotating black holes) and electric charge (see charged black holes). ... A beautiful example of an Einstein ring is the radio source B1938+666 discovered with the UK radiotelescope. ... Surface brightness is a concept used in astronomy when describing extended astronomical objects such as galaxies and nebulae. ... Angular size is a measurement of how large or small something is using rotational measurement (degrees of arc, arc_minutes, and arc-seconds). ...


History

According to general relativity, mass "warps" space-time to create gravitational fields and therefore bend light as a result. This theory was confirmed in 1919 during a solar eclipse, when Arthur Eddington observed the light from stars passing close to the sun was slightly bent, so that stars appeared slightly out of position. Unsolved problems in physics: What causes anything to have mass? Mass is a property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... In special relativity and general relativity, time and three-dimensional space are treated together as a single four-dimensional pseudo-Riemannian manifold called spacetime. ... The gravitational field is a field (physics), generated by massive objects, that determines the magnitude and direction of gravitation experienced by other massive objects. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength[1]. The elementary particle that defines light is the photon. ... Year 1919 (MCMXIX) was a common year starting on Wednesday (link will display the full calendar). ... Photo taken during the 1999 eclipse. ... One of Sir Arthur Stanley Eddingtons papers announced Einsteins theory of general relativity to the English-speaking world. ... This article is about the astronomical object. ... The Sun is the star at the center of the Solar System. ...


Einstein realized that it was also possible for astronomical objects to bend light, and that under the correct conditions, one would observe multiple images of a single source, called a gravitational lens or sometimes a gravitational mirage. However, as he only considered gravitational lensing by single stars, he concluded that the phenomenon would most likely remain unobserved for foreseeable future. In 1937, Fritz Zwicky first considered the case where a galaxy could act as a lens, something that according to his calculations should be well within the reach of observations. See also Lists of astronomical objects Category: ... A gravitational mirage is the visual impression caused by a so-called gravitational lens in space, which may include multiple images, rings, etc of background light sources. ... Fritz Zwicky (February 14, 1898 – February 8, 1974) was an American-based Swiss astronomer. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light-years in diameter and approximately 60 million light-years distant. ...


It was not until 1979 that the first gravitational lens would be discovered. It became known as the "Twin Quasar" since it initially looked like two identical quasars; it is officially named Q0957+561. This gravitational lens was discovered accidentally by Dennis Walsh, Bob Carswell, and Ray Weymann using the Kitt Peak National Observatory 2.1 meter telescope. The Twin Quasar (Double Quasar) or Old Faithful is also known as Q0957+561, or QSO 0957+561. ... The Twin Quasar (Double Quasar) or Old Faithful is also known as Q0957+561, or QSO 0957+561. ... Dennis Walsh was a British astronomer, born 12 June 1933 into a poor family in Manchester, England. ... The Kitt Peak National Observatory (KPNO) is a United States astronomical observatory located on a 2,096 m (6,880 ft) peak of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono Oodham Nation, 88 kilometres (55 miles) southwest of Tucson. ... 50 cm refracting telescope at Nice Observatory. ...


The study of gravitational lenses is an important part of the future of astronomy and astrophysics.


Cosmological applications

The most important application of gravitational lensing in cosmology is the weak lensing of galaxies. By measuring the shapes and orientations of large numbers of distant galaxies, their orientations can be averaged to measure the shear of the lensing field in any region. This, in turn, can be used to reconstruct the mass distribution in the area: in particular, the background distribution of dark matter can be reconstructed. Since galaxies are intrinsically elliptical and the weak gravitational lensing signal is small, a very large number of galaxies must be used in these surveys. These weak lensing surveys must carefully avoid a number of important sources of systematic error: the intrinsic shape of galaxies, the tendency of a camera's point spread function to distort the shape of a galaxy and the tendency of atmospheric seeing to distort images must be understood and carefully accounted for. The results of these surveys are important for cosmological parameter estimation, to better understand and improve upon the Lambda-CDM model, and to provide a consistency check on other cosmological observations. They may also provide an important future constraint on dark energy. In physics and mechanics, shear refers to a deformation that causes parallel surfaces to slide past one another (as opposed to compression and tension, which cause parallel surfaces to move towards or away from one another). ... Dark matter is a term used in astrophysics to refer to that component of the universe that is unaccounted for, unexplained or inconclusively explained, and whose existence at this time is only inferred. ... Systematic errors are biases in measurement which lead to measured values being systematically too high or too low. ... Image formation in a confocal microscope: central longitudinal (XZ) slice. ... In astronomy, the seeing disk (seeing) is a reference to the best possible angular resolution which can be achieved by an optical telescope, which is viewing the celestial sphere from within an atmosphere. ... A pie chart indicating the proportional composition of different energy-density components of the universe. ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and has strong negative pressure. ...


Strong gravitational lenses may be used to examine objects at distances at which they would not normally be visible, providing information from further back in time than otherwise possible. Also, not just the object being lensed but the lens itself can provide useful information. By inverting the lens equations information can be gathered on the mass and distribution of the lensing body. An inverse problem is the task that often occurs in many branches of science and mathematics where the values of some model parameter(s) must be obtained from the observed data. ...


The statistics of strong gravitational lenses can also be used to measure values of cosmological parameters such as the cosmological constant and the mean density of matter in the universe. Presently, the statistics do not place very strong limits on cosmological parameters, partly because the number of strong lenses found is relatively small (less than a hundred). The cosmological constant (usually denoted by the Greek capital letter lambda: Λ) was proposed by Albert Einstein as part of his theory of general relativity to achieve a stationary universe. ...


Another parameter that may come out of the study of gravitational lenses is Hubble's constant which encodes the age and size of the universe. It can be determined, in theory, by measuring two quantities: the angular separation between two images, and the time delay between these images.
There are two contributions to the time delay: Hubbles law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. ...

  1. the first is the obvious delay due to the difference in optical path length between the two rays.
  2. the second is a general relativistic effect, the Shapiro effect, that describes light rays as taking longer to traverse a region of stronger gravitation, (see: gravity well, gravitational time dilation).
    Because the two rays travel through different parts of the potential well created by the deflector, the clocks carrying the source's signal will differ by a small amount.

In optics and telecommunication, the term optical path length has the following meanings: In a medium of constant refractive index, n , the product of the geometric distance and the refractive index. ... In General relativity, the Shapiro effect, or gravitational time delay, is one of the four classic solar system tests of general relativity. ... A gravity well is the scientific/science fictional term for the distortion in space-time caused by a massive body such as a planet. ... Gravitational time dilation is a consequence of Albert Einsteins theories of relativity and related theories under which a clock at a different gravitational potential is found to tick at a different rate than ones own clock. ...

Astronomical applications

Actual gravitational lensing effects as observed by the Hubble Space Telescope in Abell 1689 - Enlarge the image to see the lensing arcs
Actual gravitational lensing effects as observed by the Hubble Space Telescope in Abell 1689 - Enlarge the image to see the lensing arcs

Gravitational lenses can be used as gravitational telescopes, because they magnify objects seen behind them. Researchers at Caltech have used the gravitational lensing afforded by the Abell 2218 cluster of galaxies to detect the most distant galaxy known (February 15, 2004) through imaging with the Hubble Space Telescope. Download high resolution version (750x938, 126 KB)Gravitational lensing. ... Download high resolution version (750x938, 126 KB)Gravitational lensing. ... Abell 1689 is a galaxy cluster in the constellation Virgo. ... California Institute of Technology The California Institute of Technology (commonly known as Caltech) is a private, coeducational university located in Pasadena, California, in the United States. ... Abell 2218 is a cluster of galaxies about 3 billion light-years away in the constellation Draco. ... February 15 is the 46th day of the year in the Gregorian Calendar. ... 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble for his discovery of galaxies outside the Milky Way and his creation of Hubbles Law, which calculates the rate at which the universe is expanding. ...


Gravitational microlensing can provide information on comparatively small astronomical objects, such as MACHOs within our own galaxy, or extrasolar planets (planets beyond the solar system). Three extrasolar planets have been found in this way, and this technique has the promise of finding Earth-mass planets around sunlike stars within the 21st century. Look up Macho in Wiktionary, the free dictionary This is a disambiguation page: a list of articles associated with the same title. ... An extrasolar planet, or exoplanet, is a planet beyond the Solar System. ... Any planet is an extremely faint light source compared to its parent star. ... The 21st century is the present century of the Anno Domini (common) era, in accordance with the Gregorian calendar. ...


Gravitational lensing can be used to calculate an estimate of the amount of dark matter contained in the lensing body.


Historical papers and references

  • Chwolson, O (1924). "Über eine mögliche Form fiktiver Doppelsterne". Astronomische Nachrichten 221: 329.
  • Einstein, Albert (1936). "Lens-like Action of a Star by the Deviation of Light in the Gravitational Field". Science 84: 506—507.
  • Renn, Jurgen; Tilman Sauer and John Stachel (1997). "The Origin of Gravitational Lensing: A Postscript to Einstein's 1936 Science paper". Science 275: 184—186. DOI:10.1126/science.275.5297.184.

Albert Einstein ( ) (March 14, 1879 – April 18, 1955) was a German-born theoretical physicist who is widely considered one of the greatest physicists of all time. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

References

  • "XFGLenses". A Computer Program to visualize Gravitational Lenses, Francisco Frutos-Alfaro
  • "G-LenS". A Point Mass Gravitational Lens Simulation, Mark Boughen.
  • Newbury, Pete, "Gravitational Lensing". Institute of Applied Mathematics, The University of British Columbia.
  • Cohen, N., "Gravity's Lens: Views of the New Cosmology", Wiley and Sons, 1988.
  • "Q0957+561 Gravitational Lens". Harvard.edu.
  • "Gravitational lensing". Gsfc.nasa.gov.
  • Bridges, Andrew, "Most distant known object in universe discovered". Associated Press. February 15, 2004. (Farthest galaxy found by gravitational lensing, using Abell 2218 and Hubble Space Telescope.)
  • Analyzing Corporations ... and the Cosmos An unusual career path in gravitational lensing.
  • "HST images of strong gravitational lenses". Harvard-Smithsonian Center for Astrophysics.
  • "A planetary microlensing event" and "A Jovian-mass Planet in Microlensing Event OGLE-2005-BLG-071" , the first extra-solar planet detections using microlensing.
  • Gravitational lensing on arxiv.org

The Associated Press, or AP, is an American news agency, the worlds largest such organization. ... February 15 is the 46th day of the year in the Gregorian Calendar. ... 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... An extrasolar planet, or exoplanet, is a planet beyond the Solar System. ...

Futher reading

  • Matthias Bartelmann and Peter Schneider (2000-08-17). "Weak Gravitational Lensing" (PDF).
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Gravitational lens

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Gravitational lens - Wikipedia, the free encyclopedia (1562 words)
A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is "bent" around a massive object (such as a massive galaxy) between the source object and the observer.
The process is known as gravitational lensing, and is one of the predictions of Albert Einstein's general relativity theory.
This gravitational lens was discovered accidentally by Dennis Walsh, Bob Carswell, and Ray Weymann using the Kitt Peak National Observatory 2.1 meter telescope.
  More results at FactBites »

 
 

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