VLBI structures of the images of the double QSO 0957 + 561

Very long baseline interferometry (VLBI) observations of the double QSO 0957 + 561 have revealed radio fine structure in the two ‘image’ components A and B. The structures are similar, both of the ‘core–jet’ type typical of many compact extragalactic radio sources. The shapes of the images put strong constraints on the mass distribution responsible for the gravitational imaging.