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Topic: Gravitational lensing

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	Gravitational Lensing
		Gravitational lensing was actually discovered for quasars before it was found for galaxies.
		This interpretation was bolstered by the discovery of a galaxy nearly in front of one of the images and a surrounding cluster of galaxies that are candidates for the intervening mass causing the lens effect.
		The stars in the foreground galaxy also seem to be acting as gravitational lenses, causing the images to change their relative brightnesses in these two photographs taken three years apart.
	csep10.phys.utk.edu /astr162/lect/galaxies/lensing.html (403 words)

	Gravitational lens - Wikipedia, the free encyclopedia (Site not responding. Last check: 2007-10-08)
		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.
		Weak lensing effects are being studied for the cosmic microwave background and strong lenses have been observed in radio and x-ray regimes as well.
		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.
	en.wikipedia.org /wiki/Gravitational_lens (1231 words)

	Gravitational lensing
		Lensing occurs when light passes nearby a massive object on its way from the source to the observer.
		The phenomenon of gravitational lensing has moved from being an interesting curiosity to a remarkable tool for astronomy in a remarkably short time.
		But the gravitational influence of sufficiently large foreground mass concentrations can be detected since lensing effects only depend on the projected mass distribution of the lens, and is, unlike other methods, independent of the constitution and dynamical state of matter.
	www.astro.su.se /~edvard/gravitationallensing.html (704 words)

	Gravitational Lensing of a Point Source - Wolfram Demonstration
		Move a point source lens of a given mass over different types of grids to see the effects of gravitational lensing.
		One of the best examples of this can be seen with "gravitational lensing." Lensing occurs when the path of light from a source (or in this case a grid of point sources) travels near a massive or energetic object, called a "lens," and bends due to the mass/energy of the lens.
		In this Demonstration the massive object is an infinitely small point of variable mass, marked with a brown dot.
	demonstrations.wolfram.com /GravitationalLensingOfAPointSource (122 words)

	Gravitational Lensing (Site not responding. Last check: 2007-10-08)
		This effect is known as gravitational lensing, and was predicted by Einstein's general theory of relativity.
		We see dramatic examples of gravitational lensing in the light from distance quasars, many billions of light years distant, which is lensed by the presence of a massive foreground galaxy or cluster to produce multiple images of the quasar.
		Gravitational microlensing monitoring programs provide a powerful new technique for studying the atmospheres and photospheres of distant stars, and for searching for extra-solar planets.
	www.astro.gla.ac.uk /users/martin/outreach/lensing.html (462 words)

	Gravitational lensing
		As a consequence of lensing, light rays that would have otherwise not reached the observer are bent from their paths and towards the observer.
		Weak lensing is a useful complement to measures of the distribution of luminous mass such as galaxy surveys.
		Lensing measures all the mass, in particular the dark matter as well as the luminous matter.
	astro.berkeley.edu /~jcohn/lens.html (1315 words)

	Cosmology: A Research Briefing
		Gravitational lensing effects are similar to those produced when a glass lens deflects the path of light rays in a camera, but the deflections are too small to be observed in a terrestrial laboratory.
		Gravitational lenses provide a unique opportunity to infer the properties of the space-time in which they are embedded, the mass distribution of the lens, and the detailed properties of the background source.
		Gravitational lensing, along with the spectroscopic absorption studies of intergalactic clouds, is one of the few techniques in cosmology in which our ability to detect the presence of matter does not require that the matter be luminous.
	www.nap.edu /readingroom/books/cosmology/4.html (3711 words)

	Gravitational Lensing
		Since lensing is a one-to-one mapping of the source and image planes it simply distorts the images formed from the acoustic oscillations in accord with the deflection angle.
		Gravitational lensing also generates a small amount of power in the anisotropies on its own but this is only noticable beyond the damping tail where diffusion has destroyed the primary anisotropies (see Plate 5a).
		Because the lensed CMB distribution is not linear in the fluctuations, it is not completely described by changes in the power spectrum.
	background.uchicago.edu /~whu/araa/node24.html (472 words)

	Gravitational Lensing (Site not responding. Last check: 2007-10-08)
		Gravitational lensing, loosely speaking, refers to the fact that light rays from a distance source are deflected and distorted by intervening mass distributions.
		The first is the so-called strong gravitational lensing, where a single background source is distorted into multiple images, spectacular giant arcs, as in CL2244 and A2218 (shown above), and, in some cases even complete rings.
		The second area is gravitational microlensing, where we observe the time-changing magnification of a background source due to lensing, please refer to my brief introduction elsewhere.
	www.jb.man.ac.uk /~smao/lens.html (238 words)

	Gravitational Lenses
		The characteristics of the gravitationally lensed image depend upon the alignment of the observer, the lens and the background object.
		The amplification, ratio of the lensed brightness of an object to its unlensed value, is larger if the line of sight passes very close to the lens.
		Lenses can amplify brightnesses by a few times, up to over a factor of 100 - this means that lenses offer the potential to "see" objects over 10 times further away.
	cassfos02.ucsd.edu /public/tutorial/GLens.html (518 words)

	Gravitational Lensing (Site not responding. Last check: 2007-10-08)
		Gravitational lensing effects arises as the light from a source is deflected by the gravitational field of an intervening mass concentration along the line of sight.
		Accurately modeling gravitational lensing requires assumptions on the underlying cosmology, on the density profile and shape of the lensing mass, and on the emitting source properties.
		Gravitational lensing statistics can be used to put constraints on the underlying cosmology.
	www.sissa.it /ap/CMB/GravLens.html (267 words)

	Gravitational Lensing (Site not responding. Last check: 2007-10-08)
		We focus here on two strong lensing statistics for clusters of galaxies: the fraction of rich Abell clusters that are critical to lensing, and the abundance of arcs in such clusters, especially the X-ray luminous ones.
		Furthermore, one needs to go beyond the weak lensing (linear) approximation as most of the observational data is concentrated in the central parts of clusters, where the lensing is strong.
		The lensing signal is complicated by the intrinsic variation in number counts due to galaxy clustering, and by additional uncertainties in the strong lensing regime.
	www.roe.ac.uk /~evk/lensing.html (562 words)

	Clusters: Gravitational lensing
		The light from distant galaxies and quasars is affected by the gravitational field of the intervening matter between us and the source, resulting in magnified or multiple images.
		The study of gravitational lensing therefore recently has become one of the most valued tools in surveying the universe and understanding its constituents and its evolutionary history.
		Analysis of systematic distortions of background galaxies (weak lensing) reveal significant structures in galaxy clusters that are not apparent from optical images.
	www.sr.bham.ac.uk /research/exgal/lens.html (437 words)

	Research page: Peter Newbury
		Gravitational lensing is easy to "forward model" when you know all about the source and deflector.
		The whole point to studying lensing systems is to determine all you can about the distribution of masses that are doing the deflecting, and about the source of the light.
		Gravitational lenses have been observed since 1979 when Walsh et al.
	www.iam.ubc.ca /~newbury/lenses/research.html (723 words)

	GRAVITATIONAL LENSING - navigatori-satellitari.cellulari-giochi.it (Site not responding. Last check: 2007-10-08)
		Gravitational Lensing in Astronomy article_prep Gravitational Lensing in Astronomy Joachim Wambsganss Astrophysikalisches Institut Potsdam An der Sternwarte 16...
		Gravitational lensing effects arises as the light from a source is deflected by the gravitational field of an...
		Gravitational lensing: theory Analytical methods to study multiple lenses: By perturbative methods, we have drawn analytical light curves for...
	navigatori-satellitari.cellulari-giochi.it /gravitational_lensing.html (336 words)

	Gravitational lensing and modified Newtonian dynamics (Site not responding. Last check: 2007-10-08)
		Gravitational lensing is most often used as a tool to investigate the distribution of (dark) matter in the universe, but, if the mass distribution is known a priori, it becomes, at least in principle, a powerful probe of gravity itself.
		Lensing observations are a more powerful tool than dynamical measurements because they allow measurements of the gravitational field far away from visible matter.
		The implied MONDian lensing formalism is consistent with general relativity, in so far as the deflection experienced by a photon is twice that experienced by a massive particle moving at the speed of light.
	www.atnf.csiro.au /pasa/18_2/mortlock1/paper (199 words)

	Basic of Gravitational Lensing - Hamilton College (Site not responding. Last check: 2007-10-08)
		Gravitational Lensing is a branch of astronomy that has developed and shown its potential as an astronomical tool within the last 20 years.
		Theory Behind the GL Gravitational Lensing occurs when an observer looks at an object or a galaxy with large mass (and therefore high gravitational potential) that has a very distant smaller object (source) behind it.
		Gravitational lensing is an exceptional branch of astrophysics in the sense that its occurrence, as well as the occurrence of many of its features Einstein’s ring, multiple images, time delays, weak lensing, were actually predicted long before they were observed.
	students.hamilton.edu /2006/kpopovic/grav_lens (1239 words)

	Cosmology -- Gravitational Lensing (Site not responding. Last check: 2007-10-08)
		The results are presented in a pair of papers; the first deals with lensing by a single screen of point masses, while the second extends the analysis to a 3-dimensional distribution of lenses.
		They found that the deflection and amplification of light propagating through a background of gravitational waves does not in general increase with the path of the light ray, unlike light propagating through the gravitational field of scalar metric - density - perturbations; the result is, unfortunately, unobservably small in almost all cases.
		They simulated weak gravitational lensing in artificial clusters grown in numerical simulations of the formation of clusters in three different cosmologies, and obtained distributions of this statistic.
	www.cita.utoronto.ca /webpages/CITA/annrep96/node30.html (976 words)

	Gravitational lensing (Site not responding. Last check: 2007-10-08)
		As a consequence of lensing, light rays that would have otherwise not reached the observer are bent from their paths and towards the observer.
		Weak lensing is a useful complement to measures of the distribution of luminous mass such as galaxy surveys.
		Lensing measures all the mass, in particular the dark matter as well as the luminous matter.
	cfa-www.harvard.edu /~jcohn/lens.html (1232 words)

	Weak Gravitational Lensing (Site not responding. Last check: 2007-10-08)
		One of the most spectacular manifestations of spacetime curvature is the phenomenon of gravitational lensing.
		Weak lensing studies have recently been made possible with the advent of wide-area cameras on optical telescopes, and sometimes suggest much larger masses for galaxy clusters than traditional measurement techniques.
		Weak lensing occurs even when the mass fluctuations are small, so it can be used to measure the mass perturbations which, according to inflationary theory, should occur on even the largest physical scales.
	www.phy.cam.ac.uk /teaching/literature/litrev024.html (193 words)

	Gravitational Lensing
		This NASA Hubble Space Telescope image of the rich galaxy cluster, Abell 2218, is a spectacular example of gravitational lensing.
		Hubble also reveals multiple imaging, a rarer lensing event that happens when the distortion is large enough to produce more than one image of the same galaxy.
		Though the gravitational light-bending process is not new, Hubble's high resolution image reveals structures within the blue-shaped galaxy that astronomers have never seen before.
	faculty.rmwc.edu /tmichalik/gravlens.htm (563 words)

	Gravitational Lensing (Site not responding. Last check: 2007-10-08)
		This so-called gravitational lensing effect can be observed with objects on all mass scales.
		The very first gravitational lens to be detected in 1979 is an example: the quasar QSO 0957+561 (right-hand image) is split by a galaxy into two images separated by 6 arc seconds.
		As it is solely determined by the mass distribution of cosmic objects and neither depends on the type of matter nor on its physical state, it has developed into one of the most versatile tools in extragalactic astronomy and cosmology.
	www.ita.uni-heidelberg.de /~msb/gravLens/index_en.html (627 words)

	Gravitational lensing brings extrasolar planets into focus (June 2004) - Physics World - PhysicsWeb
		Almost all of these were found using the "Doppler wobble" method in which the gravitational pull of a large planet swings the star around the centre of mass of the star–planet system (see "Extrasolar planets").
		However, gravitational lenses are imperfect because the rays that pass closest to the lensing mass are deflected more than rays passing further away.
		Now that gravitational lensing has secured its first new planet, we can expect the pace of discovery of extrasolar planets to increase as teams of astronomers join forces to build a network of dedicated observing facilities.
	physicsweb.org /articles/world/17/6/3/1 (1259 words)

	Gravitational Lensing: Nature's Giant Telescopes (Site not responding. Last check: 2007-10-08)
		One of the fundamental predictions of general relativity is the phenomenon of gravitational lensing, the deflection of a light ray by a massive object.
		A key feature of the gravitational lensing signal is its dependence not only on the mass of the lensing cluster but also on the relative distances between the observer, the lens and the source.
		That he should connect this problem with the important role gravitational lensing might play in resolving this question as long ago as 1937 is quite astonishing.
	serweb.oamp.fr /kneib/ast_now96 (2218 words)

	G-LenS Gravitational Lensing Simulation
		"The aim of this project was to obtain and use a knowledge of gravitational lensing to develop a computer model to simulate lensing effects on distant sources.
		Each stage of the computer model development is covered in the report, from initial ideas, through to testing the model using some of the latest gravitational* lens observations.
		It is my belief that this project has succeeded not only in producing a working simulation of a point mass gravitational lens system, but also in providing a challenge.
	www.btinternet.com /~boughen/G-LenS (231 words)

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