Hubble Space Telescope image of a galaxy acting as a gravitational lens. Here an elliptical galaxy (yellow and red) causes light from a more distant object to be seen as four faint blue images in a cross-shaped pattern. The enormous gravity of the foreground galaxy warps space nearby. This warping "bends" light, magnifying and distorting the image of the distant object. This is normally seen as arcs or a pair of images; quadruple images are rare. Studies of such objects may lead to a measurement of the density of matter in the Universe, and thus whether it will expand forever or eventually collapse.