Institution(s): 1. University of Waterloo
It is now widely accepted that the TeV emission of blazars is attenuated on cosmological scales by pair production on the extragalactic infrared background light. What happens next is more controversial. A growing body of empirical evidence supports the existence of intergalactic plasma instabilities, driven by the strong anisotropy of the TeV emission, that reprocess the gamma-ray emission of blazars into heat within the intergalactic medium, raising the temperature of voids by an order of magnitude by z=0. This novel form of feedback is intrinsically nonlocal in the sense that the location of the heating is far removed from the sources ultimately responsible, providing a qualitatively different mechanism for accreting supermassive black holes to impact their environment. I will briefly describe the key features of these plasma instabilities and then summarize the current observational case for their presence or absence.