Astronomers have spotted a near-perfect circle of light whose eerie shape was produced by a galaxy acting like an enormous lens. This "Einstein ring" is the first to be seen in infrared light, a team will report Wednesday in the Monthly Notices of the Royal Astronomical Society. The new ring, and others like it, may help researchers better gauge the distribution of galaxies in the universe's farthest reaches.
The rings are named after Albert Einstein, who predicted them as a consequence of his General Theory of Relativity. Here's how it works: The gravitational field around a star or galaxy can act like an enormous lens, bending light rays from a more distant object as they travel toward Earth. This lensing creates a kind of halo, distorting the light into several spots or arcs. If a compact and symmetrical object lies directly between a telescope and the distant light source, the arcs appear to merge into a gauzy ring. Astronomers found the first of five known Einstein rings in 1988, using radio waves.
Indeed, radio waves led astronomers to the latest--and most visually stunning--Einstein ring. Several years ago, astronomer Neal Jackson of the University of Manchester in the United Kingdom and his colleagues, using the MERLIN array of radio telescopes in England, saw arcs around a galaxy in the constellation Draco. Following up with the Hubble Space Telescope last August, Jackson's group trained the infrared-sensitive NICMOS camera on the galaxy and found a faint but intact ring surrounding it--a feat equivalent to spotting a penny held 3 kilometers away. Spotting more such rings will help astronomers pin down how mass is distributed in the distant universe, Jackson says, because gravitational lenses can precisely measure the amount of matter along a light ray's path.
"It's great to have this new capability with Hubble to find rings in the infrared," says astrophysicist Jacqueline Hewitt of the Massachusetts Institute of Technology in Cambridge, who imaged the first radio Einstein ring. And more rings will soon be revealed: A team led by astronomer Chris Impey of the University of Arizona, Tucson, has already spied two more infrared Einstein rings with Hubble, but those results aren't yet published.
An image of the ring can be viewed at the University of Manchester's MERLIN Web site.