129 research outputs found
Fluid accretion onto a spherical black hole: relativistic description versus Bondi model
We describe general-relativistically a spherically symmetric stationary fluid
accretion onto a black hole. Relativistic effects enhance mass accretion, in
comparison to the Bondi model predictions, in the case when backreaction is
neglected. That enhancement depends on the adiabatic index and the asymptotic
gas temperature and it can magnify accretion by one order in the
ultrarelativistic regime.Comment: 22 pages, accepted by the Physical Review
Gravitational redshifts in electromagnetic bursts occuring near Schwarzschild horizon
It was suggested earlier that the gravitational redshift formula can be
invalid when the effect of the backscattering is strong. It is demonstrated
here numerically, for an exemplary electromagnetic pulse that is: i) initially
located very close to the horizon of a Schwarzschild black hole and ii)
strongly backscattered, that a mean frequency does not obey the standard
redshift formula. Redshifts appear to depend on the frequency and there
manifests a backscatter-induced blueshift in the outgoing radiation.Comment: 4 pages, 2 figures. To appear in the Class. Q. Gra
Stability of relativistic Bondi accretion in Schwarzschild-(anti-)de Sitter spacetimes
In a recent paper we investigated stationary, relativistic Bondi-type
accretion in Schwarzschild-(anti-)de Sitter spacetimes. Here we study their
stability, using the method developed by Moncrief. The analysis applies to
perturbations satisfying the potential flow condition. We prove that global
isothermal flows in Schwarzschild-anti-de Sitter spacetimes are stable,
assuming the test-fluid approximation. Isothermal flows in Schwarzschild-de
Sitter geometries and polytropic flows in Schwarzschild-de Sitter and
Schwarzschild-anti-de Sitter spacetimes can be stable, under suitable boundary
conditions.Comment: 6 page
Axial gravitational waves in FLRW cosmology and memory effects
We show initial data for gravitational axial waves, that are twice
differentiable but which are not . They generate wave pulses that
interact with matter in the radiation cosmological era. This forces the
radiation matter to rotate. This rotation is permanent - it persists after the
passage of the gravitational pulse. The observed inhomogeneities of the cosmic
microwave background radiation put a bound onto discontinuities of superhorizon
metric perturbations. We explicitly show that a class of smooth initial metrics
that are at least gives rise to gravitational wave pulses that do not
interact with the background during the radiation epoch.Comment: This version matches the published article (Phys. Rev. D 96, 063523
(2017)). A note is added on interaction of axial gravitational waves with
stars' interiors, with 3 new reference
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