Superluminal Motion and Relativistic Beaming in Blazar Jets
  High resolution radio observations remain the most direct way to study the formation and evolution of radio jets associated with the accretion onto massive black holes. We report preliminary results of our seven year VLBA observational program to understand the nature of relativistic beaming in blazars and the surrounding environment of massive black holes.   Most blazars show an apparent outward flow away from an active core. However, in a few sources the motion appears inward, most likely the result of projection of a curved trajectory which bends back toward along the line of sight. The apparent motion of jet features is not always oriented along the direction separating the feature from the core, and in a few cases we have observed a clear change in the direction and velocity of a feature as it flows along the jet. In other sources, the motion appears to follow a simple ballistic trajectory. We find no simple relation between the time scales of flux density changes and apparent component velocities. 
K. I. Kellermann (1), M. L. Lister (1), D. C. Homan (1), E. Ros (2),   J. A. Zensus (2), M. H. Cohen (3), M. Russo (3), and ...