Efficiency of the Keplerian accretion in braneworld Kerr-Newman spacetimes and mining instability of some naked singularity spacetimes

Abstract

We show that the braneworld rotating Kerr-Newman black hole and naked singularity spacetimes with both positive and negative braneworld tidal charge parameter can be separated into fourteen classes according to properties of circular geodesics governing the Keplerian accretion. We determine efficiency of the Keplerian accretion disks for all braneworld Kerr-Newman spacetimes. We demonstrate occurrence of an infinitely deep gravitational potential in Kerr-Newman naked singularity spacetimes having the braneworld dimensionless tidal charge b ∈ (1/4, 1) and the dimensionless spin 1)), implying unbound efficiency of the Keplerian accretion and possibility to extract the whole naked singularity mass. Therefore, we call them braneworld "mining-unstable" Kerr-Newman naked singularity spacetimes. Fundamental restriction on the relevance of the extraordinary but fully classical phenomenon of the mining instability is given by validity of the assumption of geodesic motion of the accreting matter.

Decoding signatures of extra dimensions and estimating spin of quasars from the continuum spectrum

“…The marginally stable circular orbit corresponds to the inflection point of the effective potential, which is obtained by solving for V eff = ∂ r V eff = 0 = ∂ 2 r V eff . For the brane world black hole spacetime under consideration, the dimensionless marginally stable circular orbit, x ms is obtained by solving for the lowest real root of [127],…”

Spherical photon orbits in the field of Kerr naked singularities

“…However, the recent cosmological tests indicate presence of dark energy, probably reflected by a relict cosmological constant, that could play a significant role in astrophysical processes [4,24,43,48,51,56]. Therefore, the photon motion in the field of Kerr-de Sitter black holes, where the cosmological horizon exists along with the static radius giving the limit on the free circular motion [42,46], has been studied in [11,17,29,34,45,47]; extension to spacetimes containing a charge parameter has been discussed in [12,22,44]. There is a large number of studies related to the photon motion in generalizations of the Einstein theory, e.g., for regular black hole spacetimes of the Einstein theory combined with non-linear electrodynamics [38,55], and for black holes in alternative ap- * Electronic address: daniel.charbulak@fpf.slu.cz † Electronic address: zdenek.stuchlik@fpf.slu.cz proaches to gravity [1,3,5,35,54,60].A crucial role in the photon motion is played by the spherical photon orbits, i.e., photons moving along orbits of constant (Boyer-Lindquist) radial coordinatetheir motion constants govern the local escape cones of photons related to any family of observers, and specially the shadow (silhouette) of black holes located in front of a radiating source [7], e.g.…”

Photon motion in Kerr–de Sitter spacetimes

“…which can be solved with respect to a 2 with the same result as given by (12). However, substitution into the second derivative concurrently with the requirement y ex(ex)± (r ; a 2 ) > 0 implies…”

“…Especially relevant effects are found in the case of spherical photon orbits that can be directly related to the observational phenomena. It is quite interesting that we could expect another interesting phenomenon related to the charged Kerr-Newman or Kerr-Newman-de Sitter naked singularity spacetimes (with both the standard electric charge and the tidal charge of the braneworld models), especially in the case of the so-called mining Kerr-Newman spacetimes [12], containing a special type of equatorial stable photon orbits.…”