Pseudo-Schwarzschild description of transonic spherical accretion onto compact objects

Free access article

Issue		A&A Volume 374, Number 3, August II 2001


Page(s)		1150 - 1160
Section		Physical and chemical processes
DOI		http://dx.doi.org/10.1051/0004-6361:20010736

A&A 374, 1150-1160 (2001)
DOI: 10.1051/0004-6361:20010736

Pseudo-Schwarzschild description of transonic spherical accretion onto compact objects

Tapas K. Das¹ and A. Sarkar²

¹ Inter University Centre For Astronomy And Astrophysics, Post Bag 4 Ganeshkhind, Pune 411 007, India
e-mail: tapas@iucaa.ernet.in
² National Centre For Radio Astrophysics, TIFR, Post Bag 3 Ganeshkhind, Pune 411 007, India
e-mail: sarkar@ncra.tifr.res.in

(Received 6 March 2001/ Accepted 9 May 2001)

Abstract
A number of "modified" Newtonian potentials of various forms are available in the literature which accurately approximate some general relativistic effects important for studying accretion discs around a Schwarzschild black hole. Such potentials may be called "pseudo-Schwarzschild" potentials because they nicely mimic the space-time around a non-rotating/slowly rotating compact object. In this paper, we examine the validity of the application of some of these potentials to study the spherically symmetric, transonic, hydrodynamic accretion onto a Schwarzschild black hole. By comparing the values of various dynamical and thermodynamic accretion parameters obtained for flows using these potentials with full general relativistic calculations, we have shown that though the potentials discussed in this paper were originally proposed to mimic the relativistic effects manifested in disc accretion, it is quite reasonable to use most of the potentials in studying various dynamical as well as thermodynamic quantities for spherical accretion to compromise between the ease of handling of a Newtonian description of gravity and the realistic situations described by complicated general relativistic calculations. Also we have shown that depending on the chosen regions of parameter space spanned by specific energy ${\cal E}$ and adiabatic index $\gamma$ of the flow, one potential may have more importance than another and we could identify which potential is the best approximation for full general relativistic flow in Scwarzschild space-time for particular values of ${\cal E}$ and $\gamma$ .

Key words: accretion, accretion discs -- black hole physics -- hydrodynamics

Offprint request: Tapas K. Das, tapas@iucaa.ernet.in

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