Einstein Rings

<p>A couple of years ago, a space telescope discovered something odd about NGC 6505. The galaxy is encircled by a ring. It isn&#8217;t part of the galaxy itself. Instead, it&#8217;s an image of a background galaxy &#8211; one that&#8217;s billions of light-years farther.</p> <p>Einstein Rings are named for Albert Einstein because they were predicted by his theory of gravity. The gravity of a foreground object acts as a lens &#8211; it bends and magnifies the light of a background object.</p> <p>On small scales, gravitational lenses have revealed everything from black holes to rogue planets. Galaxies are much bigger and heavier, so they produce more dramatic lenses. Many of them create bright arcs. But when the alignment is just right, they can create a full circle.</p> <p>NGC 6505 is a good example. The galaxy is about twice the diameter of the Milky Way, and several times its mass. It&#8217;s about 600 million light-years away. The background galaxy is four billion light-years farther...