0850 + 581 - another superluminal radio source

Three 5 GHz VLBI maps of the bright core in the triple radio source 4C 58.17 associated with the quasar 0850 + 581 are presented which indicate an apparent core expansion speed of (5.3 + or - 0.8) per h c (H0 = 100 h km/s Mpc and q0 = 0.05). Attention is drawn to the fact that superluminal motion is being found in an increasing number of radio sources with extended morphologies, and the difficulties that this poses for simple beaming models are discussed. 35 references