A black-hole accretion disc as an analogue gravity model

We study spherical and nonspherical linear acoustic perturbations of the Michel flow, which describes the steady radial accretion of a perfect fluid into a nonrotating black hole. The dynamics of such perturbations are governed by a scalar wave equation on an effective curved background geometry determined by the acoustic metric, which is constructed from the spacetime metric and the particle density and four-velocity of the fluid. For the problem under consideration in this article the acoustic metric has the same qualitative features as an asymptotically flat, static and spherically symmetric black hole, and thus it represents a natural astrophysical analogue black hole.As for the case of a scalar field propagating on a Schwarzschild background, we show that acoustic perturbations of the Michel flow exhibit quasi-normal oscillations. Based on a new numerical method for determining the solutions of the radial mode equation, we compute the associated frequencies and analyze their dependency on the mass of the black hole, the radius of the sonic horizon and the angular momentum number. Our results for the fundamental frequencies are compared to those obtained from an independent numerical Cauchy evolution, finding good agreement between the two approaches. When the radius of the sonic horizon is large compared to the event horizon radius, we find that the quasi-normal frequencies scale approximately like the surface gravity associated with the sonic horizon.

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“…[14], and for recent applications to accretion flows on black hole backgrounds, see Refs. [15][16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Quasinormal acoustic oscillations in the Michel flow

2015

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“…This will help in studying the low angular momentum pseudo-Schwarzschild axisymmetric black hole accretion as a natural example of analogue gravity phenomena. It has recently been shown that the analogue surface gravity can be computed for multi-critical accretion onto astrophysical black holes (Abraham et al 2006;Das et al 2007). The present work will allow to study such phenomena for various different geometric configuration of the flow.…”

Section: Discussionmentioning

confidence: 99%

The role of flow geometry in influencing the stability criteria for low angular momentum axisymmetric black hole accretion

et al. 2012

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Using mathematical formalism borrowed from dynamical systems theory, a complete analytical investigation of the critical behaviour of the stationary flow configuration for the low angular momentum axisymmetric black hole accretion provides valuable insights about the nature of the phase trajectories corresponding to the transonic accretion in the steady state, without taking recourse to the explicit numerical solution commonly performed in the literature to study the multi-transonic black hole accretion disc and related astrophysical phenomena. Investigation of the accretion flow around a non rotating black hole under the influence of various pseudo-Schwarzschild potentials and forming different geometric configurations of the flow structure manifests that the general profile of the parameter space divisions describing the multi-critical accretion is roughly equivalent for various flow geometries. However, a mere variation of the polytropic index of the flow cannot map a critical solution from one flow geometry to the another, since the numerical domain of the parameter space responsible to produce multi-critical accretion does not undergo a continuous transformation in multi-dimensional parameter space. The stationary configuration used to demonstrate the aforementioned findings is shown to be stable under linear perturbation for all kind of flow geometries, black hole potentials, and the corresponding equations of state used to obtain the critical transonic solutions. Finally, the structure of the acoustic metric corresponding to the propagation of the linear perturbation studied are discussed for various flow geometries used.

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“…Recent works Abraham et al [2006], Das et al [2007], Pu et al [2012] demonstrate the emergence of such acoustic geometry and corresponding multiple acoustic horizons -one white hole type and two black hole type -within the general relativistic accretion of matter onto astrophysical black holes, either of the Schwarzschild or of the Kerr type. In these works, however, only a particular type of flow geometry (either flow with constant disc thickness or flow in hydrostatic equilibrium along the vertical direction) has been considered to study such emergent gravity phenomena.…”

Section: Introductionmentioning

confidence: 99%

Influence of the geometric configuration of accretion flow on the black hole spin dependence of relativistic acoustic geometry

Tarafdar

Das

2018

Int. J. Mod. Phys. D

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Linear perturbation of general relativistic accretion of low angular momentum hydrodynamic fluid onto a Kerr black hole leads to the formation of curved acoustic geometry embedded within the background flow. Characteristic features of such sonic geometry depend on the black hole spin. Such dependence can be probed by studying the correlation of the acoustic surface gravity κ with the Kerr parameter a. The κ − a relationship further gets influenced by the geometric configuration of the accretion flow structure. In this work, such influence has been studied for multitransonic shocked accretion where linear perturbation of general relativistic flow profile leads to the formation of two analogue black hole type horizons formed at the sonic points and one analogue white hole type horizon which is formed at the shock location producing divergent acoustic surface gravity. Dependence of the κ − a relationship on the geometric configuration has also been studied for monotransonic accretion, over the entire span of the Kerr parameter including retrograde flow. For accreting astrophysical black holes, the present work thus investigates how the salient features of the embedded relativistic sonic geometry may be determined not only by the background space-time, but also by the flow configuration of the embedding matter.

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A black-hole accretion disc as an analogue gravity model

Cited by 52 publications

References 83 publications

Quasinormal acoustic oscillations in the Michel flow

Quasinormal acoustic oscillations in the Michel flow

The role of flow geometry in influencing the stability criteria for low angular momentum axisymmetric black hole accretion

Influence of the geometric configuration of accretion flow on the black hole spin dependence of relativistic acoustic geometry

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