Grand illusion

Astronomers have detected the most-distant cosmic mirage ever recorded. Known as an Einstein ring, the mirage is created by the gravity of a massive foreground object—a star, galaxy, or galaxy cluster. According to the general theory of relativity, gravity bends light. A heavy object therefore acts as a lens, distorting and magnifying the appearance of a more-distant galaxy directly behind it. The lens typically bends the image into an arc, but in rare instances, when the distant galaxy and Earth are almost exactly aligned, the arc forms a nearly complete ring.

Such is the case with the newfound mirage, dubbed FOR J0332-3557, whose arc spans almost three-quarters of a circle. Using the Very Large Telescope in Paranal, Chile, researchers found that the foreground galaxy—the lens—lies 8 billion light-years from Earth. It magnifies by a factor of 13 the image of a galaxy 12 billion light-years distant, providing a distorted snapshot of the remote body as it appeared when the universe was only 12 percent of its current age.

The lens is a quiescent galaxy, 40,000 light-years in diameter and populated by old stars. In contrast, the more-distant galaxy is compact—only 7,000 light-years across—and shows recent signs of several bursts of star formation.

Rémi Cabanac, now of the Canada-France-Hawaii Telescope on Hawaii’s Mauna Kea, and his colleagues describe their work in the June (III) Astronomy & Astrophysics.

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