 In the course of analyzing this Hubble image, astronomers discovered that ESO-325 is actually a gravitational lens. This means that the focusing power of the enormous mass making up the galaxy caused the light from some distant object, probably a distant dwarf galaxy, to be deflected and magnified. As a result, the more distant galaxy appears brighter and distorted into the shape of an arc, or ring, known as an Einstein ring, because the phenomenon was first predicted by Albert Einstein. Here's an image created by adding data collected by the multi-unit spectrographic explorer instrument on the European Space Observatory, a very large telescope. This was the first test of Einstein's light-bending theory done outside of our own galaxy. It passed the test, demonstrating that the theory held across the universe and not just in the Milky Way. Here's another one. The foreground, luminous red galaxy, 4.6 billion light-years away, has about 10 times the mass of the Milky Way. The blue arc around it is the gravitationally-lensed image of a more distant galaxy, 10.9 billion light-years away. The object's name is the cosmic horseshoe. Astronomers first discovered it in 2007, using data from the Sloan Digital Sky Survey. But this Hubble image offers a much more detailed view. Although the universe is filled with galaxies, Einstein rings are a rare occurrence because it requires an almost perfect alignment of a distant galaxy with an intervening one that has enough mass to gravitationally focus the light. But a number had been found. Here are eight of them from the Sloan Digital Sky Survey and Hubble.