WHAT EVENT HORIZON TELESCOPE IMAGING CAN TEACH US ABOUT ASTROPARTICLE PHYSICS

Sera Markoff –  API/GRAPPA, Univ. of Amsterdam

The physicist John Wheeler famously said “black holes have no hair”, however astrophysical black holes do end up driving pretty « hairy » systems around themselves when they accrete surrounding material. By the time the infalling gas approaches the event horizon, it has become a turbulent plasma hotter than the solar corona that generates and amplifies strong, and strongly ordered, magnetic fields. The most dramatic outcome of this process is the launching of enormous magnetised plasma structures called ‘jets’, that can extend well beyond their host galaxy and may be tapping the rotational energy of the black hole. These jets are also of great interest for astroparticle physics as primary candidates for the origin of ultra-high energy cosmic rays, neutrinos, and gamma-rays, attaining particle energies far beyond that of the LHC. After a brief refresher about the Event Horizon Telescope (EHT) and our key results so far, I will highlight their broader implications for our understanding of high-energy particle acceleration. In particular I will focus on what can be gained by combining EHT observations with those from other multi-wavelength and eventually also multi-messenger facilities. I will also give some perspective on what is (literally) on the horizon for these topics in the coming ~decade.