Finally, in 1979, the “Twin QSO” was found: two lensed images of the same quasar. This galaxy cluster appears to be hosting two blue stars, but they are actually the same background ...

Gravitational lens was first discovered by Dennis Walsh, Bob Carswell and Ray Weymann in 1979, naming it the “Twin QSO” as their observation appeared as twin quasi-stellar objects (QSOs).