The power of jets: blazars vs galactic superluminals
  Estimates on different scales of the power of relativistic bulk motion in extragalactic and galactic jets are presented. The power in the jets and the power produced by the accretion disk are found to be roughly equal. This may suggest an important role of the magnetic field in extracting both the gravitational energy of the accreting matter and the rotational energy of the black hole. A method to derive the minimum power of jets is discussed, and used to find lower limits to the jet power of blazars and the galactic superluminal source GRS 1915+105. The matter content of jets is discussed, finding that electron positron pairs cannot be dynamically important. The jet power can initially be in the form of Poynting flux, gradually accelerating matter until equipartition between bulk motion of the particles and Poynting flux is reached. 
Gabriele Ghisellini (Osserv. Astron. di Brera, Merate, Italy)