Hubble Sees a Double Einstein Ring

by Fraser Cain on January 10, 2008

Einstein Ring. Image credit: Hubble
An Einstein Ring happens when two galaxies are perfectly aligned. The closer galaxy acts as a lens, magnifying and distorting the view of a more distant galaxy. But today astronomers announced that they’ve discovered a double Einstein Ring: three galaxies are perfectly aligned, creating a double ring around the lensing galaxy. The odds of finding something like this are pretty low. And yet… here it is.

The double Einstein Ring image was captured by the Hubble Space Telescope, and shows a central galaxy surrounding by an almost complete ring, with another fainter ring around that. Think of a bull’s-eye.

It was found by an international team of astronomers led by Raphael Gavazzi and Tommaso Treu of the University of California, Santa Barbara, and the results were presented at the 211th meeting of the American Astronomical Society in Austin, Texas.

Treu was pretty excited, “the twin rings were clearly visible in the Hubble image. When I first saw it I said ‘wow, this is insane!’ I could not believe it!”

Here’s how it works. As Einstein predicted, gravity has the power to bend light. So instead of traveling on a straight curve, light that passes close to a large mass is pulled into a curved path. When you have a foreground galaxy perfectly lined up with a background galaxy, the light from the more distant galaxy is distorted into a ring of light.

Although the background galaxy is distorted, it’s also tremendously magnified, allowing astronomers to use the foreground galaxy as a natural telescope to peer much more deeply into the Universe than they would be able to see normally.

In the case of this double ring, the foreground galaxy is 3 billion light-years away. The background galaxy that forms the first ring is 6 billion light-years away, and the second background galaxy is 11 billion-light years away. This means that the background galaxy is being seen when the Universe was less than 3 billion years old.

The alignment also allowed astronomers to measure the mass of the middle galaxy to 1 billion solar masses. This is the first time the mass of a dwarf galaxy has been measured at this kind of distance.

Original Source: Hubble News Release


Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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