Publication date: Sep 2018
Abstract:
There is strong observational evidence that many active galactic nuclei
(AGNs) harbour super-massive 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 , 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).
Authors:
Pugliese, D.; Stuchlík, Z.;