© NASA/ESA Hubble Space Telescope, NASA/Goddard Space Flight Center.
As shown above left, the gravitational influence of a massive body can bend the path of light from a distant object as it travels toward telescopes here on Earth. The image of a gravitationally lensed object can be distorted, or even appear as multiple images, as shown above right. This Hubble Space Telescope image of the gravitational lens G2237+0305 is sometimes referred to as the "Einstein Cross." The four distinct, bright spots are actually all images of the same quasar. The diffuse central spot is a foreground galaxy that has acted as a gravitational lens, bending light from the quasar so that it appears to be in four places at once. Careful measurements of lensed quasars can reveal information about the distribution of dark matter in the galaxy (or galaxy cluster) that acts as a lens. (Unit: 10)