AGN astrophysics from comparing radio and Gaia optical astrometry
  Gaia will open up a huge volume of new parameter space in which to explore
the physics of AGN and black hole evolution. We address the question as to how
far along the relativistic jets blazar radio, optical and gamma ray emission
originated. In some models the optical centroid wander should be detectable as
the relative contributions of thermal and non-thermal optical emission change.
Black holes powering AGN do not necessarily reside at the centres of their host
galaxies; they can be one member of a binary pair or they could have received a
kick after binary coalescence. For radio-loud AGN comparison of astrometric
radio and and optical positions can reveal such displacements. It is suggested
that it would be feasible to do this using Gaia and e-MERLIN for a sample of
thousands of elliptical radio galaxies.
