We constrain the BHs spin with the evaluation of the dimensionless parameter ξ, the total rotational energy extracted versus the BH mass. The energy extraction can power an outflow which can be then observed. We relate the energy extraction to the accreting configurations and the accretion processes occurring in a cluster of corotating and counter-rotating tori orbiting one central Kerr SMBH, associating ξto the accretion processes characteristics. We relate the regions of tori parameters to the energy extraction processes, binding ξto properties of light surfaces by using the bundles, relating measures in different regions of the spacetimes. We evaluate properties of the BH accretions disks, and correlate spacetimes prior and after their transition due to the energy extraction. Light surfaces are related to the generators of Killing horizons, proving limiting frequency of the stationary observers of the geometries. We consider the photon limiting curves of the stationary observers as constraints for various processes regulated by these frequencies, to relate different BH states, prior and after the energy extraction, investigating regions close to the BH horizons and rotational axis. From methodological view-point we used a naked singularity -BH correspondence defined with metric bundles to predict the BH--accretion disk system observational characteristics. The analysis points relevant BH spins a\approx0.94M, a\approx 0.7M and a\approx0.3M. We show the relation between the rotational law of the tori, the bundle characteristic frequency and the relativistic velocity defining the von Zeipel surfaces. The inferior limit on the formation of corotating is \ell/a\geq2, for counter-rotating tori \ell/a\leq -22/5 (\ell is the fluids specific angular momentum).
New closed analytical solutions for geometrically thick fluid tori around black holes: Numerical evolution and the onset of the magneto-rotational instability
Energy extraction-driven instability and horizon formation in Kerr-Newman naked singularities and their limiting cases
PDPIAS, Charusat University（PDPIAS，查鲁萨特大学）；International Centre for Space and Cosmology, School of Arts and Sciences, Ahmedabad University（艾哈迈达巴德大学文理学院国际空间与宇宙学中心）
Backreaction of Mass and Angular Momentum Accretion on Black Holes: General Formulation of the Metric Perturbations and Application to the Blandford-Znajek Process
Extending the Comisso-Asenjo Energy Extraction Mechanism to Pure Lovelock Gravity
Harbin Institute of Technology（哈尔滨工业大学）；New Uzbekistan University（新乌兹别克斯坦大学）；Institute of Fundamental and Applied Research, National Research University TIIAME（国立研究型大学TIIAME基础与应用研究所）；Tashkent University of Applied Sciences（塔什干应用科学大学）；National University of Uzbekistan（乌兹别克斯坦国立大学）
Energy Formula, Surface geometry and Energy Extraction for Kerr-Sen Black Hole
本文讨论了具有事件视界~（${\cal H}^{+}$）和柯西视界~（${\cal H}^{-}$）的\emph{Kerr-Sen black hole~(BH)}的\emph{surface energy~(${\cal E}_{s}^{\pm}$), rotational energy~(${\cal E}_{r}^{\pm}$) and electromagnetic energy~(${\cal E}_{em}^{\pm}$)}.有趣的是，我们发现\emph{sum of these three energies is equal to the mass parameter i.e. ${\cal E}_{s}^{\pm}+{\cal E}_{r}^{\pm}+{\cal E}_{em}^{\pm}={\cal M}$} .此外，根据\emph{ scale parameter ~$(ζ_{\pm})$, the distortion parameter~($ξ_{\pm}$) and a new parameter~$(σ_{\pm})$}对应的面积~（${\cal A}_{\pm}$）、角动量~（$(J)$）和电荷参数~（$Q$），我们发现\emph{mass parameter in a compact form} ${\cal E}_{s}^{\pm}+{\cal …
