Institution(s): 1. University of Waterloo
Relativistic pair beams driven by the very-high energy gamma-ray emission of accreting black holes permeate the ionized intergalactic medium, providing a novel example of a classic beam plasma instability. It is notable, however, in the extreme parameter regime in which it operates, with very large beam-target plasma density ratios and very high beam Lorentz factors, lying close to the boundary of plasma and particle physics. I will discuss the main features of the resulting beam plasma instability, provide some thoughts on its nonlinear saturation, and briefly describe some of the observational evidence that these are actually occurring.