Black holes in spacetimes with a negative vacuum energy, i.e., with an attractive cosmological constant Λ < 0, are described by the Kerr-Newman-anti-de Sitter geometry. It is proposed that if the specific angular momentum of a black hole and the attractive cosmological constant are combined appropriately, the spacetime can be considered as consisting of causally disconnected regions with opposite signature of the metric tensor, corresponding to opposite character of the geometry outside the black-hole horizons and between the horizons, respectively. No photons and test particles can cross a surface of degeneracy at a constant latitudinal coordinate, which separates the causally disconnected regions. Differences of the properties of the motion of test particles in the separated regions are discussed. They are given by the different normalization condition of the equations of motion, i.e., motion in the region with the opposite signature is of "tachyonic" nature. It is demonstrated in the simplest case of uncharged particles moving along the axis of symmetry.
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It is shown that in the field of some Kerr-Newman naked singularities a stationary spherical shell of charged dust can exist, with the specific charge being the same for all particles of the dusty shell. Gravitational attractions acting on the particles are balanced by electromagnetic repulsions in such a way that the shell is stable against radial perturbations. Particles of the shell move along orbits with constant latitude and radius. Rotation of the shell is differential. The shell is corotating relative to static observers at infinity, but it is counterrotating relative to the family of locally nonrotating observers. No such a shell can exist in the field of Kerr-Newman black holes.
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A restricted repulsive barrier exists for equatorial photon motion in some Kerr-Newman-de Sitter black-hole spacetimes, due to an interplay between the rotation of the source and the cosmological repulsion. Quite surprisingly, photons with high positive and all negative values of their impact parameter can travel freely between the black-hole horizon and the cosmological horizon in these spacetimes. The special class of the Kerr-Newman-de Sitter spacetimes with restricted repulsive barriers is represented in the space of the parameters of the geometry. The area of the parameter space corresponding to this class is largest in the case of Kerr-de Sitter spacetimes. With the charge parameter of the spacetime growing, the area shrinks. In all of these cases, the mass parameter of the spacetime must be so high that the sizes of the black-hole and cosmological horizons are comparable.
Read More
Black holes in spacetimes with a negative vacuum energy, i.e., with an
attractive cosmological constant Λ < 0, are described by the
Kerr-Newman-anti-de Sitter geometry. It is proposed that if the specific
angular momentum of a black hole and the attractive cosmological
constant are combined appropriately, the spacetime can be considered as
consisting of causally disconnected regions with opposite signature of
the metric tensor, corresponding to opposite character of the geometry
outside the black-hole horizons and between the horizons, respectively.
No photons and test particles can cross a surface of degeneracy at a
constant latitudinal coordinate, which separates the causally
disconnected regions. Differences of the properties of the motion of
test particles in the separated regions are discussed. They are given by
the different normalization condition of the equations of motion, i.e.,
motion in the region with the opposite signature is of "tachyonic"
nature. It is demonstrated in the simplest case of uncharged particles
moving along the axis of symmetry.
Read More
It is shown that in the field of some Kerr-Newman naked singularities a
stationary spherical shell of charged dust can exist, with the specific
charge being the same for all particles of the dusty shell.
Gravitational attractions acting on the particles are balanced by
electromagnetic repulsions in such a way that the shell is stable
against radial perturbations. Particles of the shell move along orbits
with constant latitude and radius. Rotation of the shell is
differential. The shell is corotating relative to static observers at
infinity, but it is counterrotating relative to the family of locally
nonrotating observers. No such a shell can exist in the field of
Kerr-Newman black holes.
Read More
A restricted repulsive barrier exists for equatorial photon motion in
some Kerr-Newman-de Sitter black-hole spacetimes, due to an interplay
between the rotation of the source and the cosmological repulsion. Quite
surprisingly, photons with high positive and all negative values of
their impact parameter can travel freely between the black-hole horizon
and the cosmological horizon in these spacetimes. The special class of
the Kerr-Newman-de Sitter spacetimes with restricted repulsive barriers
is represented in the space of the parameters of the geometry. The area
of the parameter space corresponding to this class is largest in the
case of Kerr-de Sitter spacetimes. With the charge parameter of the
spacetime growing, the area shrinks. In all of these cases, the mass
parameter of the spacetime must be so high that the sizes of the
black-hole and cosmological horizons are comparable.
Read More
