In both cases the galaxies and sources are quite distant, many hundreds of megaparsecs away from our Galaxy. Galaxy clusters can produce separations of several arcminutes. Despite being considered 'strong', the effect is in general relatively small, such that even a galaxy with a mass more than 100 billion times that of the Sun will produce multiple images separated by only a few arcseconds. There are three classes of gravitational lensing: Strong lensing Where there are easily visible distortions such as the formation of Einstein rings, arcs, and multiple images. The observer may then see multiple distorted images of the same source the number and shape of these depending upon the relative positions of the source, lens, and observer, and the shape of the gravitational well of the lensing object. More commonly, where the lensing mass is complex (such as a galaxy group or cluster) and does not cause a spherical distortion of spacetime, the source will resemble partial arcs scattered around the lens. It is usually referred to in the literature as an Einstein ring, since Khvolson did not concern himself with the flux or radius of the ring image. Petersburg physicist Orest Khvolson, and quantified by Albert Einstein in 1936. This phenomenon was first mentioned in 1924 by the St. If there is any misalignment, the observer will see an arc segment instead. If the (light) source, the massive lensing object, and the observer lie in a straight line, the original light source will appear as a ring around the massive lensing object (provided the lens has circular symmetry). Lodge, who remarked that it is 'not permissible to say that the solar gravitational field acts like a lens, for it has no focal length'. The term 'lens' in the context of gravitational light deflection was first used by O.J. Consequently, a gravitational lens has no single focal point, but a focal line. Unlike an optical lens, a point-like gravitational lens produces a maximum deflection of light that passes closest to its center, and a minimum deflection of light that travels furthest from its center. It was not until 1979 that this effect was confirmed by observation of the Twin QSO SBS 0957+561.Īn analysis of the distortion of SDP.81 caused by this effect has revealed star-forming clumps of matter. įritz Zwicky posited in 1937 that the effect could allow galaxy clusters to act as gravitational lenses.

However, this effect is more commonly associated with Einstein, who published an article on the subject in 1936. Īlthough 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. 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. 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.

The aqua circle is the light source as it would be seen if there were no lens, while white spots are the multiple images of the source (see Einstein ring).Ī gravitational lens is a distribution of matter (such as a cluster of galaxies) or a point particle 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. So redshift is actually very easy for astronomers to determine.A light source passes behind a gravitational lens (invisible point mass placed in the center of the image).

Gravitational redshift equation