Angelos Karakonstantakis (NCAC, Warsaw)
The supermassive black holes in most galaxies in the universe are powered by hot accretion flows. Both theoretical analysis and numerical simulations have indicated that, depending on the degree of magnetization, black hole hot accretion flow is divided into two modes, namely SANE (standard and normal evolution) and MAD (magnetically arrested disk). It has been an important question which mode the hot accretion flows in individual sources should belong to in reality, SANE or MAD. This issue has been investigated in some previous works but they all suffer from various uncertainties. By using the measured rotation measure (RM) values in the prototype low-luminosity active galactic nuclei in M87 at 2, 5, and 8 GHz along the jet at various distances from the black hole, combined with three-dimensional general relativity magnetohydrodynamical numerical simulations of SANE and MAD, we show in this paper that the RM values predicted by MAD are well consistent with observations, while the SANE model overestimates the RM by over two orders of magnitude and thus is ruled out.
Yuan, Feng et al., The Astrophysical Journal (2022)
Araudo Anabella (Astronomical Institute, Czech Academy of Sciences)
Ultra high energy cosmic rays (UHECRs) are charged particles with energies larger than 1 EeV. They are extragalactic but their origin remains unclear. Although observational data indicate that the arrival detection of UHECRs is coincident with starburst galaxies and Active Galactic Nuclei (AGN), the former do not have enough power to accelerate particles up to ultra high energies. On the other hand, recent theoretical advances indicate that the backflows in AGN jets can accelerate particles up to the Hillas limit. In addition, the interaction of stars with the AGN jet can serve as an effective mechanism for the jet mass loading. I will review these results and present some studies still in progress.
