Multiple quasar may indicate another gravitational lens Available to Purchase

Early last year a pair of quasars—$0957+561$ A and B—was found whose spectra were almost identical. By now it is generally believed that these twin quasars are in fact a single quasar that is multiply imaged by a gravitational lens. Recent observations and model calculations suggest that this gravitational lens effect is produced primarily by the brightest member, G1, of a cluster of galaxies, with the other members collectively producing an important effect.