New spectrophotometry of the double QSO, 0957+561 is reported, and it is shown that the absorption line region in each light path is very similar in redshift, in column density of Fe(+) and in velocity dispersion. The simplest interpretation of these results is a very massive object deflecting the light from a more distant QSO. Based on this hypothesis the differences between the emission line and continuum spectra may be explained by differential reddening, implying a reddening-corrected flux ratio B/A of approximately 2-4. This ratio is different from that found at radio wavelengths (0.7 at 6 cm), but can be explained, based on the gravitational lens hypothesis, by different flux variability at radio and optical wavelengths; however, no evidence for optical variability was found. Another difficulty may be that a point-mass gravitational lens would need to have a mass-to-light ratio greater than 1000, if it is closer than z = 0.4; at larger distances its mass would be very large (about 10 to the 14th solar masses at z = 1.2). Observations obtained so far might be explained if two massive QSOs are actually closer together than they appear to be, as a result of mutual gravitational deflection of the light.
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Wills et al. (1980) studied this question.