Hidden rings offer dark matter insight

The Hubble Space Telescope has revealed a never-before-seen optical alignment in space - a pair of glowing rings, one nestled inside the other like a bull’s-eye.

The gravitational field of an elliptical galaxy warps the light of two galaxies exactly behind it, forming an “einstein ring”. The right panel is a zoom onto the lens showing two concentric partial ring-like structures after subtracting the glare of the central, foreground galaxy Credit: NASA, ESA, and R. Gavazzi and T. Treu (University of California, Santa Barbara)

The “double Einstein ring” pattern is caused by the complex bending of light from two distant galaxies strung directly behind a foreground massive galaxy. The rarity has been found by an international team of astronomers led by Raphael Gavazzi and Tommaso Treu of the University of California.

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

The phenomenon, called gravitational lensing, occurs when a massive galaxy in the foreground bends the light rays from a distant galaxy behind it, in much the same way as a magnifying glass would. When both galaxies are exactly lined up, the light forms a circle - an “Einstein ring” - around the foreground galaxy. If another more distant galaxy lies precisely on the same sightline, a second, larger ring will appear.

More than just a novelty, this very rare phenomenon found with the Hubble Space Telescope can offer insight into dark matter, dark energy, the nature of distant galaxies, and even the curvature of the Universe. “Such stunning cosmic coincidences reveal so much about nature. Dark matter is not hidden to lensing,” added team member Leonidas Moustakas of the Jet Propulsion Laboratory in Pasadena, California. “The elegance of this lens is trumped only by the secrets of nature that it reveals.”

The discovery is part of the ongoing Sloan Lens Advanced Camera for Surveys (SLACS) program. The team reported their results at the 211th meeting of the American Astronomical Society in Texas, and the have submitted a paper has to The Astrophysical Journal.