The Hubble space telescope has snapped a cosmic bullseye – the first concentric pair of glowing rings spotted in the universe. The unique alignment of one ring nestled inside the other is the finest example of a phenomenon called an Einstein ring.
The pattern, named after the famous scientist who predicted it, is caused by gravitational lensing – the pull of a massive galaxy in the foreground bends the light from two distant galaxies hidden behind it.
Astronomers say that as well as showing a pretty pattern, the very rare phenomenon will help them learn about normally invisible substances dark matter and dark energy, plus the nature of distant galaxies and even the curvature of the universe.
The double ring was found by an international team of astronomers led by Raphael Gavazzi and Tommaso Treu of the University of California, Santa Barbara, and was announced this week at a meeting of the American Astronomical Society in Austin, Texas.
Tommaso says that they “hit the jackpot” because the odds of seeing such a special alignment are estimated to be one in 10,000.
Leonidas Moustakas of Nasa’s Jet Propulsion Laboratory, in California, said: “Such stunning cosmic coincidences reveal so much about nature. Dark matter is not hidden to lensing. The elegance of this lens is trumped only by the secrets of nature that it reveals.”
The foreground galaxy at the centre of the bullseye lies three billion light-years away. The inner ring and outer ring are made up of multiple images of two galaxies lying at much greater distances of six billion and 11 billion light-years.
Team member Adam Bolton, of the University of Hawaii, was first to identify the gravitational lens on the Sloan Digital Sky Survey – a detailed mapping of the heavens by robotic telescopes.
He said: “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!”
Gravitational lensing has previously allowed astronomers to view some of the most distant galaxies in the universe. It worked like a natural telescope to bring into view objects that would otherwise have remained invisible. Other instances are seen in the Groth Strip – a tiny piece of sky imaged by Hubble and revealed to contain 50,000 galaxies.
Photo: This Hubble close-up has had the bright central, foreground galaxy removed to show the rings more clearly. (Credit: NASA, ESA, R. Gavazzi and T. Treu).