Multitransonic Black Hole Accretion Disks with Isothermal Standing Shocks

Abstract

In this work we address the issue of shock formation in black hole accretion disks. We provide a generalized two-parameter solution scheme for multitransonic accretion and wind around Schwarzschild black holes, mainly by concentrating on accretion solutions that may contain steady, standing isothermal shocks. Such shocks conserve flow temperature by dissipating energy at the shock location. We use a vertically integrated 1.5-dimensional model to describe the disk structure, where the equations of motion apply to the equatorial plane of the central accretor, assuming the flow to be in hydrostatic equilibrium in the transverse direction. Unlike previous works in this field, our calculation is not restricted to any particular kind of postNewtonian gravitational potentials; rather, we use all available pseudo-Schwarzschild potentials to formulate and solve the equations governing the accretion and wind only in terms of the flow temperature T and specific angular momentum of the flow. The accretion flow is assumed to be nondissipative everywhere, except possibly at the shock location, if any. We observe that a significant region of parameter space spanned by {, T} allows shock formation. Our generalized formalism ensures that the shock formation is not just an artifact of a particular type of gravitational potential; rather, the inclusion of all available black hole potentials demonstrates a substantially extended zone of parameter space allowing for the possibility of shock formation. We thus arrive at the conclusion that the standing shocks are essential components of rotating, advective accretion flows of isothermal fluid around a nonspinning astrophysical black hole. We identify all possible shock solutions that may be present in isothermal disk accretion and thoroughly study the dependence of various shock parameters on fundamental dynamical variables governing the accretion flow for all possible initial boundary conditions. Types of shocks discussed in this paper may appear to be '' bright '' because of the huge amount of energy dissipation at the shock, and the quick removal of such energy to maintain isothermality may power the strong X-ray flairs recently observed to be emerging from our Galactic center. The results are discussed in connection with other astrophysical phenomena of related interest, such as the quasi-periodic oscillation behavior of galactic black hole candidates.

The Dependence of General Relativistic Accretion on Black Hole Spin

“…Thus our work is important for understanding how BH spin influences several accretion-related astrophysical phenomena, as only multitransonic flows can produce shock waves in BH accretion disks (Das 2002;Das et al 2003a and references therein).…”

Relativistic sonic geometry for isothermal accretion in the Schwarzschild metric

“…Unlike Bondi or Michel flow, axially symmetric accretion, however can have more than one transonic surfaces, see, e.g., [26][27][28] for detailed discussion from the astrophysical context. For such accretion, the number of acoustic horizons may be more than one -up to three in principle, two black hole horizons at the inner and the outer sonic points, and an acoustic white hole horizon at the shock location.…”

General Relativistic Hydrodynamic Simulations and Linear Analysis of the Standing Accretion Shock Instability around a Black Hole

“…The shock oscillation model for black hole QPOs has been investigated by many authors ( Das et al 2003a( Das et al , 2003bChakrabarti et al 2004;Aoki et al 2004;Okuda et al 2007). Recently, for example, Okuda et al (2007) performed two-dimensional pseudo-Newtonian numerical simulations of the shock oscillation in the meridian section, assuming axisymmetry and taking into account the cooling and heating of gas and radiative transport.…”