A multiply imaged quasar is a quasar that is undergoing gravitational microlensing, resulting in double, triple or quadruple images of the same quasar. The first such gravitational lens to be discovered was the double-imaged quasar Q0957+561 in 1979[1] A grouping of two or more quasars can result from a chance alignment, physical proximity, actual close physical interaction, or effects of gravity bending the light of a single quasar into two or more images.
As quasars are rare objects, the probability of three or more separate quasars being found near the same location is very low. The first true triple quasar was found in 2007 by observations at the W. M. Keck Observatory Mauna Kea, Hawaii.[2] LBQS 1429-008 was first observed in 1989 and was found to be a double quasar; itself a rare occurrence. When astronomers discovered the third member, they confirmed that the sources were separate and not the result of gravitational lensing. This triple quasar has a red shift of z = 2.076, which is equivalent to 10.5 billion light years.[3] The components are separated by an estimated 30–50 kpc, which is typical of interacting galaxies.[4] Another example of a triple quasar formed by lensing is PG1115 +08.[5]
