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Resumo: Black Holes (BHs) and Relativistic Jets from active galaxies are among the most extreme particle accelerators and very high energy (VHE) emitters in the universe. Only lately, combining theory, numerical simulations, and observations, we have started to understand the potential physical processes that prevail in the surrounds of these sources in order to explain major puzzles, like the origin of their VHE flares in gamma-rays. In regions of these sources where magnetic fields are dynamically dominating, fast magnetic reconnection is expected and thus particle acceleration driven by this process. In this seminar, I will discuss what is magnetic reconnection and present recent results that combine multidimensional magnetohydrodynamical relativistic simulations with the injection of test particles, which demonstrate how particles can be stochastically accelerated in relativistic jets and accretion flows around BHs by magnetic reconnection. We find that for jets with magnetic fields B ~ 10 G, the particles can be accelerated up to observed ultra-high energies ~10^20 eV. I will also show that these ultra-high-energy-cosmic-rays (UHECRs) are able to explain the VHE flares and the associated neutrino emission observed in the relativistic jets from active galaxies. Finally, I will discuss the implications of these results in predictions for forthcoming high energy astrophysical observatories like the Cherenkov Telescope Array (CTA).
