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Extreme physics in AGN: jets, shocks and the highest energy particles in nature

Event details of James Matthews (University of Cambridge)
Date 2 December 2020
Time 11:00 -12:00
James Matthews

Both cosmic rays and jets in active galactic nuclei (AGN) were discovered over a century ago, and, despite spectacular progress in that period, we are still far from a complete understanding of either of these extreme phenomena. In this talk, I will explore the links between the two, focussing particularly on particle acceleration in astrophysical jets and the origin of ultrahigh energy cosmic rays (UHECRs); UHECRs are protons and nuclei striking our atmosphere with energies extending beyond 1e20 eV. I will discuss ways in which particles can be accelerated to such extreme energies, focusing particularly on diffusive shock acceleration and the self-regulated cosmic ray acceleration process. Aided by hydrodynamic simulations, I will show that shocks can be formed in backflows in radio galaxies and that these shocks can accelerate particles to ultrahigh energy. I will then discuss a model in which 'dormant’ radio galaxies such as Centaurus A and Fornax A act as slowly-leaking UHECR reservoirs. These sources may also be able to explain the observed UHECR arrival directions. I will describe new work regarding the physics of particle acceleration in jets with flickering jet powers and discuss observational applications, highlighting the importance of flickering for the radio-loud/radio-quiet dichotomy and quasar emission lines. Finally, if time, I will briefly discuss some other aspects of `extreme physics’ in AGN that I am interested in.