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0957 + 561 A, B: twin quasistellar objects or gravitational lens?

0957 + 561 A, B are two QSOs of mag 17 with 5.7 arc s separation at redshift 1.405. Their spectra leave little doubt that they are associated. Difficulties arise in describing them as two distinct objects and the possibility that they are two images of the same object formed by a gravitational lens is discussed.

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Walsh, D., Carswell†, R. & Weymann‡, R. 0957 + 561 A, B: twin quasistellar objects or gravitational lens?. Nature 279, 381–384 (1979).

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