General relativistic decollimation of a jet

Abstract

The effect of defocusing introduced by spacetime curvature in a narrow conical beam of particles emanating from the vicinity of a compact mass is considered, with application to the study of jets. The deflection in particle trajectories brought about by the attraction of the central compact mass which widens the beam (the decollimation) is calculated, and reduction in the particle density and the effective luminosity in the beam by a factor of an order of magnitude is noted. Based on the assumption of geodesic motion and that collimation is decided in a region as close to the black hole as r(0) less than about 20m, it is found that, in the local rest frame, the beam starts out with a density and effective luminosity about 10 times larger, and opening angle smaller by a factor of about 2, than assumed.