We examine the accretion process onto the black hole with a string cloud background, where the horizon of the black hole has an enlarged radius $r_H=2 M/(1-α)$, due to the string cloud parameter $α\; (0 \leq α< 1)$. The problem of stationary, spherically symmetric accretion of a polytropic fluid is analysed to obtain an analytic solution for such a perturbation. Generalised expressions for the accretion rate $\dot{M}$, critical radius $r_s$, and other flow parameters are found. The accretion rate $\dot{M}$ is an explicit function of the black hole mass $M$, as well as the gas boundary conditions and the string cloud parameter $α$. We also find the gas compression ratios and temperature profiles below the accretion radius and at the event horizon. It is shown that the mass accretion rate, for both the relativistic and the non-relativistic fluid by a black hole in the string cloud model, increases with increase in $α$.
We deal with phantom energy accretion onto the Schwarzschild de-Sitter black hole. The energy flux conservation, relativistic Bernoulli equation and mass flux conservation equation are formulated to discuss the phantom accretion. We discuss the conditions for critical accretion. It is found that mass of the black hole decreases due to phantom accretion. There exist two critical points which lie in the exterior of horizons (black hole and cosmological horizons). The results for the phantom energy accretion onto the Schwarzschild black hole can be recovered by taking $Λ\rightarrow0$.
In this Letter, we examine the phantom energy accretion onto a Kehagias-Sfetsos black hole in Ho$\check{r}$ava Lifshitz gravity. To discuss the accretion process onto the black hole, the equations of phantom flow near the black hole have been derived. It is found that mass of the black hole decreases because of phantom accretion. We discuss the conditions for critical accretion. Graphically, it has been found that the critical accretion phenomena is possible for different values of parameters. The results for the Schwarzschild black hole can be recovered in the limiting case.
We investigate accretion of dark matter onto a moving Schwarzschild black hole. The dark matter is modeled by the collisionless Vlasov gas, assumed to be in thermal equilibrium at infinity. We derive an exact stationary solution and provide a compact formula for the mass accretion rate. In general, the mass accretion rate is a nonmonotonic function of the black hole velocity. A monotonic relation (the accretion rate proportional to the Lorentz factor associated with the velocity of the black hole) is obtained for high asymptotic temperatures of the gas. The derived accretion rates are relevant…
This paper deals with the steady-state polytropic fluid accretion onto a higher-dimensional Reissner-Nordstr$\ddot{o}$m black hole. We formulate the generalized mass flux conservation equation, energy flux conservation and relativistic Bernoulli equation to discuss the accretion process. The critical accretion is investigated by finding critical radius, critical sound velocity and critical flow velocity. We also explore gas compression and temperature profiles to analyze the asymptotic behavior. It is found that the results for Schwarzschild black hole are recovered when $q=0$ in four dimensio…
In this paper we study the accretion of dark energy onto a black hole in the cases that dark energy is equipped with a positive cosmological constant and when the space-time is described by a Schwarzschild-de Sitter metric. It is shown that, if confronted with current observational data, the results derived when no cosmological constant is present are once again obtained in both cases.
New developments related to our recent study of the accretion of the Vlasov gas onto a moving Schwarzschild black hole are presented. We discuss the low-temperature limit of the mas accretion rate and a simple Monte Carlo simulation used to check the results obtained in this limit. We also comment on several numerical aspects related with momentum integrals expressing the particle density current and the particle density.
We examine the steady-state spherically symmetric accretion of relativistic fluids, with a polytropic equation of state, onto a higher dimensional Schwarzschild black hole. The mass accretion rate, critical radius, and flow parameters are determined and compared with results obtained in standard four dimensions. The accretion rate, $\dot{M}$, is an explicit function of the black hole mass, $M$, as well as the gas boundary conditions and the dimensionality, $D$, of the spacetime. We also find the asymptotic compression ratios and temperature profiles below the accretion radius and at the event …
The spherically symmetric accretion onto a noncommutative (NC) inspired Schwarzschild black hole is treated for a polytropic fluid. The critical accretion rate $\dot{M}$, sonic speed $a_s$ and other flow parameters are generalised for the NC inspired black hole and compared with the results obtained for the standard Schwarzschild black holes. We also derive explicit expressions for gas compression ratios and temperature profiles below the accretion radius and at the event horizon. This analysis is a generalisation of Michel's solution to the NC geometry. Owing to the NC corrected black hole, t…
In this work we study steady and spherical relativistic dust accretion onto a static and spherically symmetric scale--dependent black hole. In particular we consider a polytropic scale--dependent black hole as a central object and obtain that the radial velocity profile and the energy density are affected when scale--dependence of the central object is taken into account and such a deviation is controlled by the so called running parameters of the scale--dependence models.
In this work, we discuss the accretion onto static spherical symmetric regular black holes for specific choices of equation of state parameter. The underlying regular black holes are charged regular black hole using Fermi-Dirac Distribution, logistic distribution, nonlinear electrodynamics, respectively and Kehagias-Sftesos asymptotically flat regular black hole. We obtain the critical radius, critical speed and squared sound speed during the accretion process near the regular black holes. We also study the behavior of radial velocity, energy density and rate of change of mass for each regular…
We derive an exact, axially symmetric solution representing stationary accretion of the relativistic, collisionless Vlasov gas onto a moving Schwarzschild black hole. The gas is assumed to be in thermal equilibrium at infinity, where it obeys the Maxwell-Jüttner distribution. The Vlasov equation is solved analytically in terms of suitable action-angle variables. We provide explicit expressions for the particle current density and accretion rates. In the limit of infinite asymptotic temperature of the gas, we recover the qualitative picture known form the relativistic Bondi-Hoyle-Lyttleton accr…
We consider the most general static spherically symmetric black hole metric. The accretion of the fluid flow around the Van der Waal's black hole is investigated and we calculate the fluid's four-velocity, the critical point and the speed of sound during the accretion process. We also analyze the nature of the universe's density and the mass of the black hole during accretion of the fluid flow. The density of the fluid flow is also taken into account. We observe that the mass is related to redshift. We compare the accreting power of the Van der Waal's black hole with Schwarzschild black hole f…
We have studied accretion of the dark matter and dark energy onto of $(n+2)$-dimensional Schwarzschild black hole and Morris-Thorne wormhole. The mass and the rate of change of mass for $(n+2)$-dimensional Schwarzschild black hole and Morris-Thorne wormhole have been found. We have assumed some candidates of dark energy like holographic dark energy, new agegraphic dark energy, quintessence, tachyon, DBI-essence, etc. The black hole mass and the wormhole mass have been calculated in term of redshift when dark matter and above types of dark energies accrete onto them separately. We have shown th…
We consider the stationary spherical accretion process of perfect fluids onto a class of spherically symmetric regular black holes corresponding to quantum-corrected Schwarzschild spacetimes. We show that the accretion rates can differ from the Schwarzschild case, suggesting that the de Sitter core inside these regular black holes, which indeed precludes the central singularity, can act for some cases as a sort of antigravitational source, decreasing the fluid's radial infall velocity in the accretion process, and for others as a gravitational enhancer, increasing the fluid flow into the black…
In this paper we study the accretion of matter onto the black holes and the shadow images obtained by an infalling accretion flow of gas in a theory of massive gravity (MG) with a spontaneously breaking Lorentz symmetry. This black hole solution is characterized by mass $M$, scalar charge $S$ and the parameter $λ$. In order to extract the astrophysical results of our analyses, firstly, we have assumed a specific range for the parameter $λ$ to constrain the scalar charge $S$ using the EHT result. To this end, we have studied the effect of the scalar charge on the intensity of the electromagneti…
This article reports results from numerical simulations of the gravitational radiation emitted from nonrotating relativistic stars as a result of the axisymmetric accretion of layers of perfect fluid matter, shaped in the form of quadrupolar shells. We adopt a {\em hybrid} procedure where we evolve numerically the polar nonspherical perturbations equations of the star coupled to a fully nonlinear hydrodynamics code that calculates the motion of the accreting matter. Self-gravity of the accreting fluid as well as radiation reaction effects are neglected.
The spherically symmetric steady accretion of polytropic perfect fluids onto a black hole is the simplest flow model that can demonstrate effects of backreaction (selfgravity). It has been discovered 16 years ago that backreaction does not influence some ("intensive") characteristics of sonic points, under suitable conditions. Herein we consider a wider class of equations of state, with polytropic indices in the range (1,2], and establish detailed boundary conditions that allow one to prove this fact. We find also numerical examples showing limits of our analytic criteria - if suitable analyti…
We study the linear stability of a nongravitating, steady-state, spherically symmetric ghost condensate accreting onto a Schwarzschild black hole using two methods. The first one is based on the conservation of the energy-momentum tensor of the perturbations (whose propagation is determined by the effective metric), and involves the determination of the sign of the time derivative of the energy of the perturbations. The second method employs the positivity of the effective potential. Both methods yield the result that the system is stable, but the second one is less practical, since it involve…
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.
The accretion disk is formed by particles moving in closed orbits around a compact object, whose physical properties and the electromagnetic radiation characteristics are determined by the space-time geometry around the compact object. In this paper, we study the physical properties and the optical appearance of the electromagnetic radiation emitted from a thin accretion disk around the two types of the black hole solution in Einstein-Æther theory. We investigate in detail the effects of the æther field on the energy flux, temperature distribution, and electromagnetic spectrum of the disk in t…
In this paper we investigate a steady accretion within the Einstein-Straus vacuole, in the presence of the cosmological constant. The dark energy damps the mass accretion rate and --- above certain limit --- completely stops the steady accretion onto black holes, which in particular is prohibited in the inflation era and after (roughly) $10^{12}$ years from Big Bang (assuming the presently known value of the cosmological constant). Steady accretion would not exist in the late phases of the Penrose's scenario - known as the Weyl curvature hypothesis - of the evolution of the Universe.
We consider accretion onto a Kiselev black hole. We obtain the fundamental equations for accretion without the back-reaction. We determine the general analytic expressions for the critical points and the mass accretion rate and find the physical conditions the critical points should fulfill. The case of polytropic gas are discussed in detail. It turns out that the quintessence parameter plays an important role in the accretion process.
We obtain an analytic solution for accretion of a gaseous medium with a adiabatic equation of state ($P=ρ$) onto a Reissner-Nordström black hole which moves at a constant velocity through the medium. We obtain the specific expression for each component of the velocity and present the mass accretion rate which depends on the mass and the electric charge. The result we obtained may be helpful to understand the physical mechanism of accretion onto a moving black hole.
The stationary, spherically symmetric accretion of dark energy onto a Schwarzschild black hole is considered in terms of relativistic hydrodynamics. The approximation of an ideal fluid is used to model the dark energy. General expressions are derived for the accretion rate of an ideal fluid with an arbitrary equation of state p=p(ρ) onto a black hole. The black hole mass was found to decrease for the accretion of phantom energy. The accretion process is studied in detail for two dark energy models that admit an analytical solution: a model with a linear equation of state, p=α(ρ-ρ_0), and a Cha…
We construct a simple accretion model of a rotating pressureless gas sphere onto a Schwarzschild black hole. We show how to build analytic solutions in terms of Jacobi elliptic functions. This construction represents a general relativistic generalisation of the Newtonian accretion model first proposed by Ulrich (1976). In exactly the same form as it occurs for the Newtonian case, the flow naturally predicts the existence of an equatorial rotating accretion disc about the hole. However, the radius of the disc increases monotonically without limit as the flow reaches its maximum allowed angular …
We investigate spherically symmetric, steady state, adiabatic accretion onto a Tangherlini-Reissner-Nordstrom black hole in arbitrary dimensions by using $D$-dimensional general relativity. We obtain basic equations for accretion and determine analytically the critical points, the critical fluid velocity, and the critical sound speed. We lay emphasis on the condition under which the accretion is possible. This condition constrains the ratio of mass to charge in a narrow limit, which is independent of dimension for large dimension. This condition may challenge the validity of the cosmic censors…
The equations governing general relativistic, spherically symmetric, hydrodynamic accretion of polytropic fluid onto black holes are solved in Schwarzschild metric to investigate some of the transonic properties of the flow. Only stationary solutions are discussed. For such accretion, it has been shown that real physical sonic points may form {\it even for flow with $γ< {4/3}$ or $γ> {5/3}$}. Behaviour of some flow variables in the close vicinity of the event horizon are studied as a function of specific energy and polytropic index of the flow.
We present a new geometrical approach to the study of accretion flows onto rotating (Kerr) black holes. Instead of Boyer-Lindquist coordinates, the standard choice in all existing numerical simulations in the literature, we employ the simplest example of a horizon adapted coordinate system, the Kerr-Schild coordinates. This choice eliminates boundary ambiguities and unphysical divergent behavior at the event horizon. Computations of Bondi-Hoyle accretion onto extreme Kerr black holes, performed here for the first time, demonstrate the key advantages of this procedure. We argue it offers the be…
We consider spherically symmetric accretion onto a small, possibly primordial, black hole residing at the center of a neutron star governed by a cold nuclear equation of state (EOS). We generalize the relativistic Bondi solution for such EOSs, approximated by piecewise polytropes, and thereby obtain analytical expressions for the steady-state matter profiles and accretion rates. We compare these rates with those found by time-dependent, general relativistic hydrodynamical simulations upon relaxation and find excellent agreement. We consider several different candidate EOSs, neutron star masses…
We study time evolution of sub-Keplerian transonic accretion flows onto black holes using a general relativistic numerical simulation code. We perform simulations in Schwarzschild spacetime. We first compare one-dimensional simulation results with theoretical results and validate the performance of our code. Next, we present results of axisymmetric, two-dimensional simulation of advective flows. We find that even in this case, for which no complete theoretical analysis is present in the literature, steady state shock formation is possible.
Radial steady-state accretion of polytropic matter is investigated under cylindrical symmetry in the Levi-Civita background metric. The model can be considered as a cylindrical analog of Bondi accretion in strong gravitational field. As a byproduct of this study, the issue of defining the line mass density is addressed and the role of the metric free parameters is discussed on the example of physical observables. The form of radial accretion equations is insensitive to the structure of the interior solution. Accordingly, the accretion solution analysis can be limited to a special Wilson form o…
We study effects of heating by dark matter (DM) annihilation on black hole gas accretion. We observe that, for reasonable assumptions about DM densities in spikes around supermassive black holes, as well as DM masses and annihilation cross-sections within the standard WIMP model, heating by DM annihilation may have an appreciable effect on the accretion onto Sgr A$^*$ in the Galactic center. Motivated by this observation we study the effects of such heating on Bondi accretion, i.e. spherically symmetric, steady-state Newtonian accretion onto a black hole. We consider different adiabatic indice…
The accretion of test fluids flowing onto a black hole is investigated. Particularly, by adopting a dynamical Hamiltonian approach, we are capable to find the critical points for various cases of black hole in conformal gravity. In these cases, we have analyzed the general solutions of accretion employing the isothermal equations of state. The steady state and spherically symmetric accretion of different test fluids onto the conformal gravity black hole has been considered. Further, we have classified these flows in the context of equations of state and the cases of conformal gravity black hol…
The choked accretion model consists of a purely hydrodynamical mechanism in which, by setting an equatorial to polar density contrast, a spherically symmetric accretion flow transitions to an inflow-outflow configuration. This scenario has been studied in the case of a (non-rotating) Schwarzschild black hole as central accretor, as well as in the non-relativistic limit. In this article, we generalize these previous works by studying the accretion of a perfect fluid onto a (rotating) Kerr black hole. We first describe the mechanism by using a steady-state, irrotational analytic solution of an u…
We study the adiabatic accretion process of ordinary baryonic gas onto spherically symmetric black holes in Einstein-Maxwell-scalar theory, with two parameters $α$ and $β$ in the coupling term. Especially, we demonstrate the range of the transonic points in terms of the charge-to-mass ratio squared and the dimensionless coordinate radius, in two important classes of black holes as examples. Further, we find that the two coupling parameters give modifications to the mass accretion rate at different orders of the sound speed at infinity. We also present their different effects on the temperature…
We formulate and solve the problem of spherically symmetric, steady state, adiabatic accretion onto a Schwarzschild-like black hole obtained recently. We derive the general analytic expressions for the critical points, the critical velocity, the critical speed of sound, and subsequently the mass accretion rate. The case for polytropic gas is discussed in detail. We find the parameter characterizing the breaking of Lorentz symmetry will slow down the mass accretion rate, while has no effect on the gas compression and the temperature profile below the critical radius and at the event horizon.
We investigate the dynamical behavior of phantom energy near stringy magnetically charged black hole. For this purpose, we derive equations of motion for steady-state spherically symmetric flow of phantom energy onto the stringy magnetically charged black hole. It is found that phantom energy accreting onto black hole decreases its mass. Further, the location of critical points of accretion is explored, which yields mass to charge ratio. This ratio implies that accretion process cannot transform a black hole into an extremal black hole or a naked singularity, hence cosmic censorship hypothesis…
Quantum gravity corrections to accretion onto a Schwarzschild black hole are considered in the context of asymptotically safe scenario. The possible positions of the critical points are discussed and the general conditions for critical points are obtained. The explicit expressions for matter density compression and temperature profile both below the critical radius and at the event horizon are derived. For polytropic matter, we determine the corrected temperature and the integrated flux resulting from quantum gravity effects at the event horizon, which might be as a test of asymptotically safe…
We present an analytic solution for accretion of a gaseous medium with adiabatic equation of state onto a charged dilaton black hole which moves at a constant velocity. We determine the four-velocity of accreted flow and find that it possesses axial symmetry. We obtain the particle number density and the accretion rate which depend on the mass, the magnetic charge, and the dilation of black hole, meaning that these parameters take important roles in the process of accretion. Possible theoretical and observational constraints on the parameter related to the dilation are discussed. The results m…
The transonic phenomenon of black hole accretion and the existence of the photon sphere are the characteristics of strong gravitational fields near a black hole horizon. In this work, we study spherical accretion flow onto a general parametrized spherically symmetric black hole spacetimes. For this purpose, we analyze the accretion process of various perfect fluids, such as the isothermal fluid of ultra-stiff, ultra-relativistic, and sub-relativistic types and polytropic fluid, respectively. The influences of extra parameters beyond the Schwarzschild black hole in the general parameterized sph…
In this paper we investigate the problem of ordinary baryonic matter accretion onto the noncommutative geometry inspired Schwarzschild black hole. The fundamental equations governing the spherically symmetric steady state matter accretion are deduced. These equations are seen to be modified due to the presence of noncommutativity. The matter accretion rate is computed and is found to increase rapidly with the increase in strength of the noncommutative parameter. The sonic radius reduces while the sound speed at the sonic point increases with the increase in the strength of noncommutativity. Th…
Accreting neutron stars can power a wide range of astrophysical phenomena including short- and long-duration gamma-ray bursts, ultra-luminous X-ray sources, and X-ray binaries. Numerical simulations are a valuable tool for studying the accretion-disk--magnetosphere interaction that is central to these problems, most clearly for the recently discovered transitional millisecond pulsars. However, magnetohydrodynamic (MHD) methods, widely used for simulating accretion, have difficulty in highly magnetized stellar magnetospheres, while force-free methods, suitable for such regions, cannot include t…
The Johannsen-Psaltis spacetime describes a rotating black hole with parametric deviations from the Kerr metric. By construction this spacetime explicitly violates the no-hair theorems. Rotating black hole solutions in any modified theory of gravity could be written in terms of the Johannsen-Psaltis metric. We examined the accretion of gas onto a black hole described by the static limit of this spacetime. We employed a potential that generalises the Paczynski-Wiita potential to the static Johannsen-Psaltis metric. Our analysis utilised a recent pseudo-Newtonian formulation of the dynamics arou…
The accretion process onto spinning objects in Kerr spacetimes is studied with numerical simulations. Our results show that accretion onto compact objects with Kerr parameter (characterizing the spin) $|a| < M$ and $|a| > M$ is very different. In the super-spinning case, for $|a|$ moderately larger than $M$, the accretion onto the central object is extremely suppressed due to a repulsive force at short distance. The accreting matter cannot reach the central object, but instead is accumulated around it, forming a high density cloud that continues to grow. The radiation emitted in the accretion …
Simplified assumptions about the thermodynamics of the electrons are normally employed in general-relativistic magnetohydrodynamic (GRMHD) simulations of accretion onto black holes. To counter this, we have developed a self-consistent approach to study magnetised and radiatively cooled two-temperature accretion flows around a Kerr black hole in two spatial dimensions. The approach includes several heating processes, radiative cooling, and a coupling between the electrons and the ions via Coulomb interaction. We test our approach by performing axisymmetric GRMHD simulations of magnetised tori a…
Dissipations, e.g. heat flow and bulk and shear viscosities, cause the transport of energy, momentum and angular momentum, which is the essence of accretion of matters onto celestial objects. Dissipations are usually described by the Fourier and Navier-Stokes laws ("classic laws" of dissipations). However the classic laws result in an infinitely fast propagation of dissipations. In relativistic formulation, the classic laws of dissipations violate the causality, and hence no relativistic theory of accretion flow onto celestial object is formulated. In this short report, we summarize the causal…
We describe the concept of a shallow-water setup for simulation of gas accretion onto a black hole in the mode of a quasi-spherical accretion. The bottom for the shallow-water container must have the funnel-shaped curvilinear concavo-convex shape. We calculate the configuration surface of the properly shaped bottom that simulates precisely the Newtonian or pseudo-Newtonian gravitational potentials. Like the spatial part of the Schwarzchild metric, the funnel's surface metric has a (removable) singularity at the finite distance from the funnel's center and places the certain funnel's depth whic…
The $5 - 20 M_\odot$ dark objects in X-ray binary systems and the $10^5 - 10^9 M_\odot$ dark objects in galactic nuclei are currently thought to be the Kerr black holes predicted by General Relativity. However, direct observational evidence for this identification is still elusive, and the only viable approach to confirm the Kerr black hole hypothesis is to explore and rule out any other possibility. Here we investigate the final stages of the accretion process onto generic compact objects. While for Kerr black holes and for more oblate bodies the accreting gas reaches the innermost stable cir…
We present the results of an exhaustive numerical study of fully relativistic non-axisymmetric Bondi-Hoyle accretion onto a moving Schwarzschild black hole. We have solved the equations of general relativistic hydrodynamics with a high-resolution shock-capturing numerical scheme based on a linearized Riemann solver. The numerical code was previously used to study axisymmetric flow configurations past a Schwarzschild hole. We have analyzed and discussed the flow morphology for a sample of asymptotically high Mach number models. The results of this work reveal that initially asymptotic uniform f…
Bondi-type accretion onto a Kerr black hole in the kinetic regime
Instytut Fizyki Teoretycznej, Uniwersytet Jagielloński（雅盖隆大学）；Instituto de Física y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo（米却肯圣尼古拉斯自治大学）
We consider a general stationary solution and derive the general laws for accretion of rotating perfect fluids. For non-degenerate and degenerate Fermi and Bose fluids we derive new effects that mimic the center-of-mass-energy effect of two colliding particle in the vicinity of horizons. Non-degenerate fluids see their chemical potential grow arbitrarily and ultra-relativistic Fermi fluids see their specific enthalpy and Fermi momentum grow arbitrarily too while the latter vanishes gradually for non-relativistic Fermi fluids. For degenerate Bose fluids two scenarios remain possible as the flui…
