Relating Kerr SMBHs in active galactic nuclei to RADs configurations

Abstract

There is strong observational evidence that many active galactic nuclei (AGNs) harbour supermassive black holes (SMBHs), demonstrating multi-accretion episodes during their life-time. In such AGNs, corotating and counterrotating tori, or strongly misaligned disks, as related to the central Kerr 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 attractor, tori are coplanar and axi-symmetric. Many of the RAD aspects are governed mostly by the spin of the Kerr geometry. We classify Kerr black holes (BHs) due to their dimensionless spin, according to possible combinations of corotating and counterrotating equilibrium or unstable (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 Kerr BH dimensionless spin a governing the classification in whole the black hole range 0 ≤ a ≤ M , uniquely constrained by the RAD properties. The spin values are remarkably close providing an accurate characterization of the Kerr attractors based on the RAD properties. RAD dynamics is richer in the spacetimes of high spin values. 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 X-ray 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 spacetimes in relation to astrophysical phenomena arising in different stages of AGNs life that could be observed by the planned X-ray satellite observatory ATHENA (Advanced Telescope for High ENergy Astrophysics).

RADs energetics and constraints on emerging tori collisions around super-massive Kerr black holes

“…Our results show that even in the simplest but effective set-up considered here, the presence of such "screening bubbles" cannot be considered as a general universal property of any spinning attractor, but on the contrary, the systems composed by orbiting multi structures (within the symmetry conditions fixed here) must undergo strict constraints on the relative tori rotation and they strongly depend on the dimensionless spin of the central Kerr attractor. This result remarkably sets, for the first time to our knowledge, a strong unifying framework for studying of an orbiting multiple configuration and its BH attractor [30]. Specifically, we show that only four BHs classes, distinguished according to their dimensionless spin, can host specific RAD configurations, in dependence on periods of the life of the attractor and the RAD.…”

“…Finally, we emphasize that for the tori couples with inner corotating tori, in particular for the cases (ii) and (iii) considered in Eq. (12), the possibility of penetration of matter into ergoregion Σ + , or the formation of extended toroidal matter configurations contained in this region, can occur; we refer to [26,89,27,28,32,30,31] for a detailed discussion on this possibility, while in Sec. (A) we briefly add further considerations on this aspect.…”

“…From observational view-point a relevant aspect of the BHs astrophysics related to the interaction of central BH with the RADs consists in the possibility that a RAD would have been indeed observed so far and identified as the case of one accretion torus orbiting its central BH attractor: this possibility, also discussed in [30], challenges the description of RAD as an whole orbiting toroidal structure despite its internal complex dynamics. In order to do this in [27], the definitions of RAD elongation and thickness, and the RAD distribution of angular momentum were provided, while in [30] these systems were carefully related to the characteristics of the SMBHs attractors. This new framework can be particularly interesting and can have important implications in the processes analyzed in [98,99,100,101,102,103,104], where the hypothesis of different accretion stages are claimed as ground to justify the SMBH masses at high redshift, and can have a relevant role in the studies of the X-ray screening emission where an accreting torus is supposed to be adjacent to an obscuring torus (i.e.…”

“…The paper [29] focused on the case of two tori as "seed" for larger configurations. The RAD configurations were then discussed in more detailed form in two works [32,30]. The fourth fundamental study of the RAD is related to their energetics and it is subject of the present paper.…”

“…This finding thus represents a precise guidance and gives directions to orient any studies featuring possible screening effects in this framework. The constraints provided here are very restrictive-we argue that, by considering different processes leading to RAD formation, some RAD configurations are likely to be formed around some specific attractors in some periods of the RAD-BH life [30,27,28,32,33].…”