Figure 11.4: A Hubble space telescope image of the galaxy cluster 0024+1654 acting as a gravitational lens. The mass in the foreground cluster of galaxies (the bright, diffuse images in the center) acts as a gravitational lens for a more distant galaxy. The geometry of the lens (not a point) is such that multiple images of the distant galaxy are produced close to the radius of the Einstein ring. The images are distorted into arcs.