This process is called gravitational lensing and in many cases can be described in analogy to the deflection of light by (e.g. a galaxy) acts as a physical lens which bends the light. 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 towards 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. This review summarises the theory of gravitational lensing, its main current applications and representative results achieved so far. Hubble was the first telescope to resolve details within these multiple banana-shaped arcs. BASIC CONCEPTS OF GRAVITATIONAL LENSING 2.1 The Thin Gravitational Lens. The standard gravitational lens theory is valid for weak stationary gravitational fields. The deflection has well-known observable effects, such as multiple images, magnification of images, and time delays for propagation of light along the paths forming different images. The phenomenon at the root of gravitational lensing is the deflection of light by gravitational fields predicted by Einstein's general relativity, in the weak-field limit. Strong Lensing Effects • Einstein Rings/Arcs (aka Chowlson Ring) ¾a deformation of the light from a source into a ring through gravitational deflection of the source’s light by a lens ¾Occurs when the source, lens and observer are all aligned ¾We see an arc when the object, lens, and observer are not perfectly aligned. The Mechanics of a Gravitational Lens . Gravitational Lensing An interesting prediction of general relativity is that light does not just travel in a straight line, but its path is bent by gravity. Galaxy cluster Abell 383 is a gravitational lens. Figure 2: the galaxy cluster: Abell 2218 (Richard, 2008). It is like having an extra lens that is the size of the galaxy cluster. The density of plasma in galaxies usually decreases with radius, thus, the refraction deflection (third term in equation 7 ) is opposite to the gravitational deflection, since the refractive index of plasma is smaller than 1. Gravitational lensing is the name for the bending of light by gravity, as the source of gravity (e.g. 2 Looking through a lensing galaxy cluster, Hubble can see fainter and more distant galaxies than otherwise possible. In the first, starting from the equation of geodesic deviation, the equations of thin and extended gravitational lensing are … It has two parts. Gravitational Lensing In general relativity, the presence of matter (energy density) can curve spacetime, and the path of a light ray will be deflected as a result. The homogeneous plasma (second term in equation 7) increases the deflection angle of gravitational lensing. Figure 1: Gravitational lensing, exagerated scale (Calcada, 2011). The concept behind gravitational lensing is simple: everything in the universe has mass and that mass has a gravitational pull. 2. In this respect, Gravitational Microlensing is a scaled-down version of Gravitational Lensing, where an intervening object (like a galaxy cluster) is used to focus light coming from a … F. Chamizo Gravitational lensing 17 IntroductionComplexElliptical IElliptical IIDisks For (planar) elliptic galaxies with isothermal density. gravitational lensing can manifest itself as a group of stretched out, lensed galaxies forming arcs around a cluster. The gravitational lensing results in multiple images of the original galaxy each with a characteristically distorted banana-like shape or even into rings. Gravitational lensing not only distorts the image of a background galaxy, it can amplify its light. glass) lenses in optics. One famous example is Abell 2218 as shown in Figure 2. 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