Umberto Maio, Massimo Dotti, Margarita Petkova, Albino Perego, Marta Volonteri
Mass and spin are often referred to as the two `hairs’ of astrophysical black holes, as they are the only two parameters needed to completely characterize them in General Relativity. The interaction between black holes and their environment is where complexity lies, as the relevant physical processes occur over a large range of scales. This is particularly relevant in the case of super-massive black holes (SMBHs), hosted in galaxy centers and surrounded by swirling gas and various generations of stars, that compete with the SMBH for gas consumption, and affect the thermodynamics of the gas itself. How dynamics and thermodynamics in such fiery environment affect the angular momentum of the gas accreted onto SMBHs, and hence black hole spins is uncertain. We explore the interaction between SMBHs and their environment during active phases through simulations of circum-nuclear discs (CND) around black holes in quasars hosted in the remnants of galaxy mergers. These are the first 3D (sub-)parsec resolution simulations that study the evolution of the SMBH spin explicitly including the effects of star formation, stellar winds, supernova feedback, and radiative transfer. This approach is crucial to investigate the angular momentum of the material that is accreted by the hole. We find that maximally rotating black holes are slightly spun down, and slow-rotating holes are spun up, leading to upper-intermediate equilibrium values of the spin parameter (~0.7-0.9). Our results suggest that, when quasar activity is driven by mergers of galaxies of similar sizes, stellar feedback does not induce strong chaos in the gas inflow, and that most SMBHs at the end of the quasar epoch have substantial spins….
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