Key points are not available for this paper at this time.
The galaxy responsible for causing multiple gravitational lens images of QSO Q0957+561 has been reobserved spectroscopically and a more accurate redshift of 0.36 was obtained. In addition, detailed models of the gravitational lens effect were computed. These models, which can explain all optical and radio data for the system, predict delays of up to five years between variations in the A and B images (with A preceding B). It is suggested that the third image is rather faint and located close to the center of the lens galaxy; it is possible that this third image contributes to the observed galaxy core. The possibility that this system can be used to measure the Hubble constant is discussed.
Young et al. (Sun,) studied this question.