AAS: Seeing double
Sometimes a picture can be more profound than it looks. This unassuming black-and-white image shows something never seen before – a double ‘Einstein ring’ created by a chance cosmic alignment.
Look closely – you should see not only a bright, nearly circular ring, but also fainter, interrupted arcs of light outside it. That second concentric ring is what makes it a double Einstein ring.
The regular Einstein rings are pretty cool in themselves. They’re optical illusions of a sort, created when light from a distant object (like a galaxy) gets bent by the gravity of a second object that lies along the line of sight between us and the first object. Tommaso Treu, of the University of California Santa Barbara, likens it to holding up a wine glass and looking at a candle through its stem; the distortions in the glass smear out the candle flame into arc-like shapes.
There are only about 50 regular Einstein rings known to date, and Treu and his colleagues were recently hunting for more. And that’s when they stumbled across the double ring. The geometry is complicated: first there’s us; then, 3 billion light-years away, the ‘lens’ which is some object like a massive galaxy; then, 6 billion light-years away, another galaxy whose light has been smeared by the lens to create the inner, bright ring; and finally, 11 billion light-years away, the galaxy whose light has been similarly smeared into the outer, fainter arcs.
It’s a rare alignment, but Treu thinks there may be more out there. Future space missions could potentially spot as many as 50 of the double rings, he says. And with that, astronomers might be able to use the rings to start answering questions about how matter and energy is distributed throughout the universe.