Relating Kerr SMBHs in Active Galactic Nuclei to RAD configurations

Abstract

There is strong observational evidence that many active galactic nuclei (AGNs) harbour supermassive black holes (SMBHs), demonstrating multi-accretion episodes during their lifetime. In such AGNs, corotating and counterrotating tori, or strongly misaligned disks, as related to the central SMBH spin, can report traces of the AGNs evolution. Here we concentrate on aggregates of accretion disks structures, ringed accretion disks (RADs) orbiting a central Kerr SMBH, assuming that each torus of the RADs is centered in the equatorial plane of the BH, tori are coplanar and axisymmetric. Many RAD aspects are governed mostly by the Kerr geometry spin. We classify Kerr BHs due to their dimensionless spin, according to possible combinations of corotating and counterrotating equilibrium or accreting tori composing the RADs. The number of accreting tori in RADs cannot exceed n=2. We present list of 14 characteristic values of the BH spin a governing the classification in the BH range 0<a<M, constrained by the RAD properties. The spins are remarkably close providing an accurate characterization of the Kerr BHs based on the RAD properties. RAD dynamics is richer in the spacetimes of high spins. One of the critical predictions states that a RAD tori couple formed by an outer accreting corotating and an inner accreting counterrotating torus is expected to be observed only around slowly spinning (a<0.46M) BHs. The analysis strongly binds the fluid and BH characteristics providing indications on the situations where to search for RADs observational evidences. Obscuring and screening tori, possibly evident as traces in Xray spectrum emission, are strongly constrained, eventually ruling out many assumptions used in the current investigations of the screening effects. We expect relevance of our classification of Kerr BHs in relation to AGNs phenomena that could be observed by the Xray satellite ATHENA.