Figure 13-48 Gravitational Lensing of Extremely Distant Galaxies (a) Schematic of how a gravitational lens works. Light from the distant object changes direction due to the gravitational attraction of the intervening galaxy and underlying dark matter. The more distant galaxy appears in different places than it actually is. (b) Three examples of gravitational lensing: (1) The blue ring is a galaxy that has been lensed by the redder elliptical galaxy; (2) a pair of bluish images of the same object lensed symmetrically by the brighter, redder galaxy between them; and (3) the lensed object appears as a blue arc under the gravitational influence of the group of four galaxies. (c) This image shows the gravitational lensing of a distant galaxy and a distant quasar by a cluster of galaxies between them and us. (d) This cluster contains over a thousand galaxies. The red shows the cluster’s hot gas, while the blue is its dark matter, determined by gravitational lensing. (e) A mechanism proposed to explain the separation of gas and dark matter in clusters like (d). (f) Gravitational lensing by this filament of dark matter between two clusters of galaxies reveals its presence.