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1.
The secular evolution of the purely general relativistic low angular momentum accretion flow around a spinning black hole is shown to exhibit hysteresis effects. This confirms that a stationary shock is an integral part of such an accretion disc in the Kerr metric. The equations describing the space gradient of the dynamical flow velocity of the accreting matter have been shown to be equivalent to a first order autonomous dynamical systems. Fixed point analysis ensures that such flow must be multi-transonic for certain astrophysically relevant initial boundary conditions. Contrary to the existing consensus in the literature, the critical points and the sonic points are proved not to be isomorphic in general, they can form in a completely different length scales. Physically acceptable global transonic solutions must produce odd number of critical points. Homoclinic orbits for the flow possessing multiple critical points select the critical point with the higher entropy accretion rate, confirming that the entropy accretion rate is the degeneracy removing agent in the system. However, heteroclinic orbits are also observed for some special situation, where both the saddle type critical points of the flow configuration possesses identical entropy accretion rate. Topologies with heteroclinic orbits are thus the only allowed non-removable degenerate solutions for accretion flow with multiple critical points, and are shown to be structurally unstable. Depending on suitable initial boundary conditions, a homoclinic trajectory can be combined with a standard non-homoclinic orbit through an energy preserving Rankine-Hugoniot type of stationary shock, and multi-critical accretion flow then becomes truly multi-transonic. An effective Lyapunov index has been proposed to analytically confirm why certain class of transonic flow cannot accommodate shock solutions even if it produces multiple critical points. 相似文献
2.
《New Astronomy》2015
We introduce a novel formalism to investigate the role of the spin angular momentum of astrophysical black holes in influencing the behavior of low angular momentum general relativistic accretion. We propose a metric independent analysis of axisymmetric general relativistic flow, and consequently formulate the space and time dependent equations describing the general relativistic hydrodynamic accretion flow in the Kerr metric. The associated stationary critical solutions for such flow equations are provided and the stability of the stationary transonic configuration is examined using an elegant linear perturbation technique. We examine the properties of infalling material for both prograde and retrograde accretion as a function of the Kerr parameter at extremely close proximity to the event horizon. Our formalism can be used to identify a new spectral signature of black hole spin, and has the potential of performing the black hole shadow imaging corresponding to the low angular momentum accretion flow. 相似文献
3.
We examine the behaviour of accretion flow around a rotating black hole in presence of cooling. We obtain global flow solutions
for various accretion parameters that govern the accreting flow. We show that standing isothermal shock wave may develop in
such an advective accretion flow in presence of cooling. This shocked solution has observational consequences as it successfully
provides the possible explanations of energy spectra as well as generation of outflows/jets of various galactic and extra-galactic
black hole candidates. We study the properties of isothermal shock wave and find that it strongly depends on the cooling efficiency.
We identify the region in the parameter space spanned by the specific energy and specific angular momentum of the flow for
standing isothermal shock as a function of cooling efficiencies and find that parameter space gradually shrinks with the increase
of cooling rates. Our results imply that accretion flow ceases to contain isothermal shocks when cooling is beyond its critical
value. 相似文献
4.
《New Astronomy》2016
Stationary, multi-transonic, integral solutions of hydrodynamic axisymmetric accretion onto a rotating black hole have been compared for different geometrical configurations of the associated accretion disc structures described using the polytropic as well as the isothermal equations of state. Such analysis is performed for accretion under the influence of generalised post Newtonian pseudo Kerr black hole potential. The variations of the stationary shock characteristics with black hole spin have been studied in details for all the disc models and are compared for the flow characterised by the two aforementioned equations of state. Using a novel linear perturbation technique it has been demonstrated that the aforementioned stationary solutions are stable, at least upto an astrophysically relevant time scale. It has been demonstrated that the emergence of the horizon related gravity like phenomena (the analogue gravity effects) is a natural consequence of such stability analysis, and the corresponding acoustic geometry embedded within the transonic accretion can be constructed for the propagation of the linear acoustic perturbation of the mass accretion rate. The analytical expression for the associated sonic surface gravity κ has been obtained self consistently. The variations of κ with the black hole spin parameter for all different geometric configurations of matter and for various thermodynamic equations of state have been demonstrated. 相似文献
5.
黑洞吸积的双模式特征 总被引：1，自引：0，他引：1
黑洞吸积必定是跨声速的。对于静态、绝热吸积流,比能量E、比角动量L和质量吸积率M都是空间的常量。跨声速解的非奇异条件,F(E,L,M)=0,使独立参数减为只有两个。对于一对给定的E和L的符合条件E_c>E>E_(Barr)的值(这里E_c是一临界值,E_(Barr)是引力和离心力的联合势垒),上述非奇异条件给出两个不同的吸积率值,对应着两个不同的吸积流声速点位置。然而,物理上合理的整体解却是唯一的,它总是使两个吸积率值中之较小者得到实现。 对于一个不转动的黑洞,吸积以两种模式之一进行。一是类球吸积或称Bondi吸积,角动量的影响和相对论效应均微不足道;另一是盘吸积,这两个因素起决定性作用。两种模式之间的转换是基于声速点位置的间断性跳跃,而这种跳跃是由吸积流参数(例如角动量)的连续变化所引发。Bondi吸积可称为高态而盘吸积为低态,因为前者总对应着较高的吸积率。 随时间变化的吸积流很可能在这两种模式之间来回振荡,呈现出周期性或准周期性或无规则行为。这可以用来解释天鹅座X-1和若干活动星系核的光变现象,从而为黑洞的存在提供有力的观测依据。 相似文献
6.
7.
Santabrata Das Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》2008,389(1):371-378
We study the dynamical structure of a cooling dominated rotating accretion flow around a spinning black hole. We show that non-linear phenomena such as shock waves can be studied in terms of only three flow parameters, namely the specific energy , the specific angular momentum (λ) and the accretion rate of the flow. We present all possible accretion solutions. We find that a significant region of the parameter space in the plane allows global accretion shock solutions. The effective area of the parameter space for which the Rankine–Hugoniot shocks are possible is maximum when the flow is dissipation-free. It decreases with the increase of cooling effects and finally disappears when the cooling is high enough. We show that shock forms further away when the black hole is rotating compared to the solution around a Schwarzschild black hole with identical flow parameters at a large distance. However, in a normalized sense, the flow parameters for which the shocks form around the rotating black holes are produced shocks closer to the black hole. The location of the shock is also dictated by the cooling efficiency in that higher the accretion rate , the closer is the shock location. We believe that some of the high-frequency quasi-periodic oscillations may be due to the flows with higher accretion rate around the rotating black holes. 相似文献
8.
Orhan Dönmez 《Astrophysics and Space Science》2006,305(2):187-196
In this paper, perturbations of an accretion disk by a star orbiting around a black hole are studied. We report on a numerical experiment, which has been carried out by using a parallel-machine code originally developed by Dönmez (2004). An initially steady state accretion disk near a non-rotating (Schwarzschild) black hole interacts with a “star”, modeled as an initially circular region of increased density. Part of the disk is affected by the interaction. In some cases, a gap develops and shock wave propagates through the disk. We follow the evolution for order of one dynamical period and we show how the non-axisymetric density perturbation further evolves and moves downwards where the material of the disk and the star become eventually accreted onto the central body. When the star perturbs the steady state accretion disk, the disk around the black hole is destroyed by the effect of perturbation. The perturbed accretion disk creates a shock wave during the evolution and it loses angular momentum when the gas hits on the shock waves. Colliding gas with the shock wave is the one of the basic mechanism of emitting the X-rays in the accretion disk. The series of supernovae occurring in the inner disk could entirely destroy the disk in that region which leaves a more massive black hole behind, at the center of galaxies. 相似文献
9.
假设位于黑洞赤道面上做圆形轨道运动的吸积盘是几何薄、光学厚的.利用光子追踪法计算在Kerr度规下的光子运动轨迹,通过数值计算研究薄吸积盘的相对论谱线轮廓及成像.在大角度观测时,吸积盘下表面的光子对谱线轮廓及成像的影响是显著的. 相似文献
10.
Ipsita Mandal Arnab K. Ray Tapas K. Das 《Monthly notices of the Royal Astronomical Society》2007,378(4):1400-1406
The stationary, spherically symmetric, polytropic and inviscid accretion flow in the Schwarzschild metric has been set-up as an autonomous first-order dynamical system, and it has been studied completely analytically. Of the three possible critical points in the flow, the one that is physically realistic behaves like the saddle point of the standard Bondi accretion problem. One of the two remaining critical points exhibits the strange mathematical behaviour of being either a saddle point or a centre-type point, depending on the values of the flow parameters. The third critical point is always unphysical and behaves like a centre-type point. The treatment has been extended to pseudo-Schwarzschild flows for comparison with the general relativistic analysis. 相似文献
11.
Santabrata Das 《Monthly notices of the Royal Astronomical Society》2007,376(4):1659-1670
We investigate the behaviour of dissipative accreting matter close to a black hole, as this provides important observational features of galactic and extragalactic black hole candidates. We find a complete set of global solutions in the presence of viscosity and synchrotron cooling. We show that advective accretion flow can have a standing shock wave and the dynamics of the shock is controlled by the dissipation parameters (both viscosity and cooling). We study the effective region of the parameter space for standing as well as oscillating shock. We find that the shock front always moves towards the black hole as the dissipation parameters are increased. However, viscosity and cooling have opposite effects in deciding the solution topologies. We obtain two critical cooling parameters that separate the nature of the accretion solution. 相似文献
12.
Giuseppe Lanzafame D. Molteni & Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》1998,299(3):799-804
Viscous Keplerian discs become sub-Keplerian close to a black hole since they pass through sonic points before entering into it. We study the time evolution of polytropic viscous accretion discs (both in one- and two-dimensional flows) using smoothed particle hydrodynamics. We discover that for a large region of the parameter space spanned by energy, angular momentum and polytropic index, when the flow viscosity parameter is less than a critical value, standing shock waves are formed. If the viscosity is very high then the shock wave disappears. In the intermediate viscosity, the disc oscillates very significantly in the viscous time-scale. Our simulations indicate that these centrifugally supported high density regions close to a black hole play an active role in the flow dynamics, and consequently, the radiation dynamics. 相似文献
13.
The broad X-ray iron line observed in many active galactic nuclei spectra is thought to originate from the accretion disc surrounding the putative supermassive black hole. We show here how to perform the analytical integration of the geodesic equations that describe the photon trajectories in the general case of a rotating black hole (Kerr metric), in order to write a fast and efficient numerical code for modelling emission line profiles from accretion discs. 相似文献
14.
Julien Malzac 《Astrophysics and Space Science》2007,311(1-3):149-159
In the last decade multi-wavelength observations have demonstrated the importance of jets in the energy output of accreting
black hole binaries. The observed correlations between the presence of a jet and the state of the accretion flow provide important
information on the coupling between accretion and ejection processes. After a brief review of the properties of black hole
binaries, I illustrate the connection between accretion and ejection through two particularly interesting examples. First,
an INTEGRAL observation of Cygnus X-1 during a ‘mini-’ state transition reveals disc jet coupling on time scales of orders
of hours. Second, the black hole XTEJ1118+480 shows complex correlations between the X-ray and optical emission. Those correlations
are interpreted in terms of coupling between disc and jet on time scales of seconds or less. Those observations are discussed
in the framework of current models. 相似文献
15.
《New Astronomy》2019
For low angular momentum axially symmetric accretion flow maintained in hydrostatic equilibrium along the vertical direction, the value of the Mach number at the critical points deviates from unity, resulting in the non-isomorphism of the critical and the sonic points. This introduces several undesirable complexities while analytically dealing with the stationary integral accretion solutions and the corresponding phase portraits. We propose that the introduction of an effective dynamical sound speed may resolve the issue in an elegant way. We linear perturb the full spacetime-dependent general relativistic Euler and the continuity equations governing the structure and the dynamics of accretion disc in vertical equilibrium around Schwarzschild black holes and identify the sonic metric embedded within the stationary background flow. Such metric describes the propagation of the linear acoustic perturbation inside the accretion flow. We construct the wave equation corresponding to that acoustic perturbation and find the speed of propagation of such perturbation. We finally show that the ordinary thermodynamic sound speed should be substituted by the speed of propagation of the linear acoustic wave which has been obtained through the dynamical perturbation. Such substitution will make the value of Mach number at the critical point to be equal to unity. Use of the aforementioned effective sound speed will lead to a modified stationary disc structure where the critical and the sonic points will be identical. 相似文献
16.
D. Molteni G. Gerardi V. Teresi 《Monthly notices of the Royal Astronomical Society》2006,365(4):1405-1408
We discuss a special case of formation of axisymmetric shocks in the accretion flow of ideal gas on to a Schwarzschild black hole: when the total energy of the flow is negative. The result of our analysis enlarges the parameter space for which these steady shocks are exhibited in the accretion of gas rotating around relativistic stellar objects. Since Keplerian discs have negative total energy, we guess that, in this energy range, the production of the shock phenomenon might be easier than in the case of positive energy. So our outcome reinforces the view that sub-Keplerian flows of matter may significantly affect the physics of the high energy radiation emission from black hole candidates. We give a simple procedure to obtain analytically the position of the shocks. The comparison of the analytical results with the data of one-dimensional (1D) and two-dimensional (2D) axisymmetric numerical simulations confirms that the shocks form and are stable. 相似文献
17.
We investigate the variation of the gas and the radiation pressure in accretion disks during the infall of matter to the black hole and its effect to the flow. While the flow far away from the black hole might be non-relativistic, in the vicinity of the black hole it is expected to be relativistic behaving more like radiation. Therefore, the ratio of gas pressure to total pressure (β) and the underlying polytropic index (γ) should not be constant throughout the flow. We obtain that accretion flows exhibit significant variation of β and then γ, which affects solutions described in the standard literature based on constant β. Certain solutions for a particular set of initial parameters with a constant β do not exist when the variation of β is incorporated appropriately. We model the viscous sub-Keplerian accretion disk with a nonzero component of advection and pressure gradient around black holes by preserving the conservations of mass, momentum, energy, supplemented by the evolution of β. By solving the set of five coupled differential equations, we obtain the thermo-hydrodynamical properties of the flow. We show that during infall, β of the flow could vary up to ∼300%, while γ up to ∼20%. This might have a significant impact to the disk solutions in explaining observed data, e.g. super-luminal jets from disks, luminosity, and then extracting fundamental properties from them. Hence any conclusion based on constant γ and β should be taken with caution and corrected. 相似文献
18.
A. M. Beloborodov 《Monthly notices of the Royal Astronomical Society》1998,297(3):739-746
We calculate the structure of the accretion disc around a rapidly rotating black hole with a super-Eddington accretion rate. The luminosity and height of the disc are reduced by the advection effect. In the case of large viscosity parameter, α>0.03, the accretion flow deviates strongly from thermodynamic equilibrium and overheats in the central region. With increasing accretion rate, the flow temperature steeply increases, reaches maximum, and then falls off. The maximum is achieved in the advection-dominated regime of accretion. The maximum temperature in the disc around a massive black hole of M =108 M⊙ with α=0.3 is of order 3×108 K. The discs with large accretion rates can emit X-rays in quasars as well as in galactic black hole candidates. 相似文献
19.
We present the results of an exhaustive numerical study of fully relativistic non-axisymmetric Bondi–Hoyle accretion on to 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 black hole. We have analysed and discussed the flow morphology for a sample of asymptotically high Mach number models. The results of this work reveal that initially asymptotic uniform flows always accrete on to the hole in a stationary way, which closely resembles the previous axisymmetric patterns. This is in contrast with some Newtonian numerical studies where violent flip-flop instabilities were found. As discussed in the text, the reason can be found in the initial conditions used in the relativistic regime, as they cannot exactly duplicate the previous Newtonian setups where the instability appeared. The dependence of the final solution on the inner boundary condition as well as on the grid resolution has also been studied. Finally, we have computed the accretion rates of mass and linear and angular momentum. 相似文献
20.
The normal mode oscillations of thin accretion disks around black holes and other compact objects are analyzed and contrasted with those in stars. For black holes, the most robust modes are gravitationally trapped near the radius at which the radial epicyclic frequency is maximum. Their eigenfrequencies depend mainly on the mass and angular momentum of the black hole. The fundamental g-mode has recently been seen in numerical simulations of black hole accretion disks. For stars such as white dwarfs, the modes are trapped near the inner boundary (magnetospheric or stellar) of the accretion disk. Their eigenfrequencies are approximately multiples of the (Keplerian) angular velocity of the inner edge of the disk. The relevance of these modes to the high frequency quasi-periodic oscillations observed in the power spectra of accreting binaries will be discussed. In contrast to most stellar oscillations, most of these modes are unstable in the presence of viscosity (if the turbulent viscosity induced by the magnetorotational instability acts hydrodynamically). 相似文献