Post-Newtonian Spherically Symmetrical Accretion

Abstract

The objetive of this work is to investigate the influence of the corrections to the spherical symmetrical accretion of an infinity gas cloud characterized by a polytropic equation into a massive object due to the post-Newtonian approximation.The post-Newtonian corrections to the critical values of the flow velocity, sound velocity and radial distance are obtained from the system of hydrodynamics equations in spherical coordinates. The critical point in the post-Newtonian approximation accretion does not correspond to the transonic point like in Newtonian theory. An equation for the Mach number was obtained as a function of a dimensionless radial coordinate. It was considered that the ratio of the sound velocity far the massive body and the speed of light was of order $a_{\infty }/c=10^{-2}$. The analysis of the solution led to following results: the Mach number for the Newtonian and post-Newtonian accretion have practically the same values for radial distances of order of the critical radial distance; by decreasing the radial distance the Mach number for the Newtonian accretion is bigger than the one for the post-Newtonian accretion; the Mach number increases by decreasing the ratio of the specific heats; the difference between the Newtonian and post-Newtonian Mach numbers when the ratio $a_{\infty }/c\ll 10^{-2}$ is insignificant. The effect of the correction terms in post-Newtonian Bernoulli equation is more perceptive for the lowest values of the radial distance, and the solutions for $a_{\infty }/c>10^{-2}$ does not lead to a continuous inflow and outflow velocity at the critical point. A comparison of the solutions with those that follow from a relativistic Bernoulli equation shows that the dependence of the Mach number with the radial distance of the former is bigger than the post-Newtonian ones.

arXiv commentTo appear in PRD

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