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Convergence tests based on the Michel (cross symbols) and Fishbone–Moncrief (plus symbols) solutions, as described in text. The thin solid line represents a function proportional to N⁻², depicting a perfect second order convergence.
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We investigate relativistic low angular momentum accretion of inviscid perfect fluid onto a Schwarzschild black hole. The simulations are performed with a general-relativistic, high-resolution (second-order), shock-capturing, hydrodynamical numerical code. We use horizon-penetrating Eddington-Finkelstein coordinates to remove inaccuracies in region...
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Mazharimousavi and Halilsoy [S. H. Mazharimousavi and M. Halilsoy, Mod. Phys. Lett. A31, 1650192 (2016)] recently proposed wormhole solutions in f(R)-gravity that satisfy energy conditions but are unstable. We show here that stability could still be achieved for thin-shell wormholes obtained by gluing the wormholes in f(R)-gravity with the exterior...
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... For example, some authors have taken into account the fluid's self gravity by solving the coupled Einstein-Euler system in spherical symmetry, either with an analytical treatment (Malec 1999) or by performing numerical simulations (Lora-Clavijo et al. 2013). Some works have considered the extension of a Bondi-like solution by introducing a low angular momentum fluid (Abramowicz & Zurek 1981;Proga & Begelman 2003;Mach et al. 2018), finding a transition between a quasi-spherical accretion flow and the formation of a thick torus in the equatorial plane. Similarly, there have been works studying spherical accretion in the presence of magnetic fields, either assuming a central dipole (Toropin et al. 1999), or by including a three-dimensional, large-scale weak magnetic field (e.g. ...
In this work, we revisit the steady-state, spherically symmetric gas accretion problem from the non-relativistic regime to the ultrarelativistic one. We first perform a detailed comparison between the Bondi and Michel models, and show how the mass accretion rate in the Michel solution approaches a constant value as the fluid temperature increases, whereas the corresponding Bondi value continually decreases, the difference between these two predicted values becoming arbitrarily large at ultrarelativistic temperatures. Additionally, we extend the Michel solution to the case of a fluid with an equation of state corresponding to a monoatomic, relativistic gas. Finally, using general relativistic hydrodynamic simulations, we study spherical accretion on to a rotating black hole, exploring the influence of the black hole spin on the mass accretion rate, the flow morphology and characteristics, and the sonic surface. The effect of the black hole spin becomes more significant as the gas temperature increases and as the adiabatic index γ stiffens. For an ideal gas in the ultrarelativistic limit (γ = 4/3), we find a reduction of 10 per cent in the mass accretion rate for a maximally rotating black hole compared to a non-rotating one, while this reduction is of up to 50 per cent for a stiff fluid (γ = 2).
... For example, some authors have taken into account the fluid's self gravity by solving the coupled Einstein-Euler system in spherical symmetry, either with an analytical treatment (Malec 1999) or by performing numerical simulations (Lora-Clavijo et al. 2013). Some works have considered the extension of a Bondi-like solution by introducing a low angular momentum fluid (Abramowicz & Zurek 1981;Proga & Begelman 2003;Mach et al. 2018), finding a transition between a quasi-spherical accretion flow and the formation of a thick torus in the equatorial plane. Similarly, there have been works studying spherical accretion in the presence of magnetic fields, either assuming a central dipole (Toropin et al. 1999), or by including a three-dimensional, large-scale weak magnetic field (e.g. ...
In this work we revisit the steady state, spherically symmetric gas accretion problem from the non-relativistic regime to the ultra-relativistic one. We first perform a detailed comparison between the Bondi and Michel models, and show how the mass accretion rate in the Michel solution approaches a constant value as the fluid temperature increases, whereas the corresponding Bondi value continually decreases, the difference between these two predicted values becoming arbitrarily large at ultra-relativistic temperatures. Additionally, we extend the Michel solution to the case of a fluid with an equation of state corresponding to a monoatomic, relativistic gas. Finally, using general relativistic hydrodynamic simulations, we study spherical accretion onto a rotating black hole, exploring the influence of the black hole spin on the mass accretion rate, the flow morphology and characteristics, and the sonic surface. The effect of the black hole spin becomes more notorious as the gas temperature increases and as the adiabatic index $\gamma$ stiffens. For an ideal gas in the ultra-relativistic limit ($\gamma=4/3$), we find a reduction of 10 per cent in the mass accretion rate for a maximally rotating black hole as compared to a non-rotating one, while this reduction is of up to 50 per cent for a stiff fluid ($\gamma=2$).
... Even though the choked accretion model does not account directly for fluid rotation, the assumption of an anisotropic density field is motivated precisely as a way to introduce indirectly one of the effects of fluid rotation and angular momentum conservation, namely, the existence of a well-defined symmetry axis (the rotation axis) and the accompanying flattening of the accreting fluid that results in an equator-to-poles density gradient (see, e.g. [37,38]). ...
... Since the flow is stationary, the equation ∇ µ J µ = 0 gives ( 2 sin θJ r ) ,r + ( 2 sin θJ θ ) ,θ + ( 2 sin θJ φ ) ,φ = 0. (38) Therefore, the mass accretion rate (current flux) associated with J through a two-surface S is given bẏ ...
... I, this density profile is motivated as a way to introduce the axisymmetric anisotropy associated with fluid rotation. In particular, it has been shown that low angular momentum fluids accreting onto a central massive object give rise to a quasi-spherical, oblate density distribution, as long as the angular momentum is sufficiently low as to avoid encountering the centrifugal barrier [37,38]. ...
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 (nonrotating) Schwarzschild black hole as central accretor, as well as in the nonrelativistic 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 ultrarelativistic perfect fluid, obeying a stiff equation of state. We then use hydrodynamical numerical simulations in order to explore a more general equation of state. Analyzing the effects of the black hole’s rotation on the flow, we find in particular that the choked accretion inflow-outflow morphology prevails for all possible values of the black hole’s spin parameter, showing the robustness of the model.
... In general, astrophysical black holes are believed to possess nonzero spin angular momentum [62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81], and such spin angular momentum (the Kerr parameter a) assumes a vital role in influencing the various characteristic features of accretion-induced astrophysical phenomena [39]. Attempts to study relativistic low angular momentum accretion of inviscid perfect fluids using hydrodynamical codes [82] bridging analytics and numerical relativity are significant in this context. There have also been recent numerical works regarding accretion onto spinning black holes investigating parameters that might influence the stability, stationarity, and other longtime behaviors of the flow [83][84][85]. ...
We illustrate how the formation of energy-preserving shocks for polytropic accretion and temperature-preserving shocks for isothermal accretion are influenced by various geometrical configurations of general relativistic, axisymmetric, low angular momentum flow in the Kerr metric. Relevant pre-and postshock states of the accreting fluid, both dynamical and thermodynamic, are studied comprehensively. Self-gravitational backreaction on the metric is not considered in the present context. An elegant eigenvalue-based analytical method is introduced to provide qualitative descriptions of the phase orbits corresponding to stationary transonic accretion solutions without resorting to involved numerical schemes. Effort is made to understand how the weakly rotating flow behaves in close proximity to the event horizon and how such "quasiterminal" quantities are influenced by the black hole spin for different matter geometries. Our main purpose is thus to mathematically demonstrate that, for non-self-gravitating accretion, separate matter geometries, in addition to the corresponding space-time geometry, control various shock-induced phenomena observed within black hole accretion disks. We expect to reveal how such phenomena observed near the horizon depend on the physical environment of the source harboring a supermassive black hole at its center. We also expect to unfold correspondences between the dependence of accretion-related parameters on flow geometries and on black hole spin. Temperature-preserving shocks in isothermal accretion may appear bright, as a substantial amount of rest-mass energy of the infalling matter gets dissipated at the shock surface, and the prompt removal of such energy to maintain isothermality may power the x-ray/IR flares emitted from our Galactic Center.
... We account for the change in black hole mass and spin during the accretion of mass-energy through the black hole horizon, and we evolve the spacetime as a sequence of Kerr solutions. The stellar structure is described using a slowly rotating, quasi-spherical flow, with the relativistic solution for the Bondi-Michel radial dependence of density and the specific angular momentum concentrated at the equator ; see also, e.g., Mach et al. 2018). Our simulations utilize the changing Kerr metric coefficients and black hole growth, which we have implemented within the HARM code (High Accuracy Relativistic Magnetohydrodynamics; Gammie et al. 2003). ...
We compute the evolution of a quasi-spherical, slowly rotating accretion flow around a black hole, whose mass and spin evolve adequately to transfer of mass and energy through the horizon. Our model is relevant for a central engine driving a long gamma-ray burst (GRB) that originates from the collapse of a massive star. The computations of a GRB engine in a dynamically evolving spacetime metric are important specifically due to the transient nature of the event, in which a huge amount of mass is accreted and changes the fundamental black hole parameters - its mass and spin - during the process. We discuss the results in the context of the angular momentum magnitude of the collapsing star. We also study the possible formation and evolution of shocks in the envelope, which may temporarily affect accretion. Our results are important for the limitations on the mass and spin range of black holes detected independently by electromagnetic observations of GRBs and gravitational waves. We speculate on the possible constraints for the final masses and spins of these astrophysical black holes. It is shown that the most massive black holes are not formed in a powerful GRB explosion if the cores of their progenitors were only weakly rotating. © 2018. The American Astronomical Society. All rights reserved..
We consider agglomerates of misaligned, pressure supported tori orbiting a Schwarzschild black hole. A leading function is introduced, regulating the toroids distribution around the central static attractor – it enables us to model the misaligned tori aggregate as a single orbiting (macro-)configuration. We first analyse the leading function for purely hydrodynamical perfect fluid toroids. Later, the function is modified for presence of a toroidal magnetic field. We study the constraints on the tori collision emergence and the instability of the agglomerates of misaligned tori with general relative inclination angles. We discuss the possibility that the twin peak high-frequency quasi-periodic oscillations (HF-QPOs) could be related to the agglomerate inner ringed structure. The discrete geometry of the system is related to HF-QPOs considering several oscillation geodesic models associated to the toroids inner edges. We also study possible effect of the tori geometrical thickness on the oscillatory phenomena.
For certain geometric configuration of matter falling onto a rotating black hole, we develop a novel linear perturbation analysis scheme to perform the stability analysis of stationary integral accretion solutions corresponding to the steady state low angular momentum, inviscid, barotropic, irrotational, general relativistic accretion of hydrodynamic fluid. We demonstrate that such steady states remain stable under linear perturbation, and hence the stationary solutions are reliable to probe the black hole spacetime using the accretion phenomena.We report that a relativistic acoustic geometry emerges out as the consequence of such stability analysis procedure. We study various properties of that sonic geometry in detail. We construct the causal structures to establish the one to one correspondences of the sonic points with the acoustic black hole horizons, and the shock location with an acoustic white hole horizon. The influence of the spin of the rotating black holes on the emergence of such acoustic spacetime has been discussed.
