Einstein’s rings in space

In a 1936 paper, Albert Einstein described how the gravitational field from a massive object can warp space and thereby deflect light. In special cases, the light from a distant object can be so distorted that it creates a complete ring known as an “Einstein ring.” The distortion maps the distribution of matter creating the warp and brightens the light source to make otherwise too-faint galaxies visible.

“An Einstein ring is one of the most dramatic demonstrations of the general theory of relativity in the cosmos,” said Adam Bolton of the Harvard-Smithsonian Center for Astrophysics (CfA). “It provides an unique opportunity to study the most massive galaxies in the universe.”

The optical illusion created by warped space is called gravitational lensing. It is nature’s equivalent of having a giant magnifying lens in space that bends and amplifies the light of more distant objects. In gravitational lensing, light from a distant galaxy can be deflected by an intervening galaxy to create an arc or multiple separate images. When both galaxies are exactly lined up, the light forms a bull’s-eye pattern, called an Einstein ring, around the foreground galaxy.

Astronomers now have combined two powerful astronomical assets, the Sloan Digital Sky Survey (SDSS) and NASA’s Hubble Space Telescope, to identify 19 new gravitational lens galaxies, adding significantly to the approximately 100 gravitational lenses previously known. By studying the arcs and rings produced by these lens candidates, the astronomers can precisely measure the mass of the foreground galaxies. Among these 19, they also have found eight new Einstein rings. Only three such rings had previously been seen in visible light.

These newly discovered lenses come from an ongoing project called the Sloan Lens ACS Survey (SLACS). A team of astronomers, led by Adam Bolton of CfA and Leon Koopmans of the Kapteyn Astronomical Institute in the Netherlands, selected its candidate lenses from among several hundred thousand optical spectra of elliptical galaxies in the Sloan Digital Sky Survey. They then used the sharp eyes of Hubble’s Advanced Camera for Surveys (ACS) to make the confirmation.