Einstein Duble brings us news that astronomers using the Hubble Telescope have discovered an extremely rare double Einstein Ring. Occasionally, galaxies or other bright objects are located in such a way that they are behind another galaxy when viewed from Earth. When light from the further galaxy passes a sufficiently massive closer galaxy, the path of the light is bent inward from all sides, creating a "ring" effect. In this case, not one, but two galaxies are directly behind the foreground galaxy, so the gravitational lens produces two distinct rings. Quoting Presscue: "The distribution of dark matter in the foreground galaxies that is warping space to create the gravitational lens can be precisely mapped. In addition, the geometry of the two Einstein rings allowed the team to measure the mass of the middle galaxy precisely to be a value of 1 billion solar masses. The team reports that this is the first measurement of the mass of a dwarf galaxy at cosmological distance (redshift of z=0.6)."