A1 Refereed original research article in a scientific journal

On the Eddington limit for relativistic accretion discs




AuthorsPavel Abolmasov, Anna Chashkina

Publication year2015

Journal:Monthly Notices of the Royal Astronomical Society

Volume454

Issue4

First page 3432

Last page3444

Number of pages13

ISSN0035-8711

DOIhttps://doi.org/10.1093/mnras/stv2229


Abstract

Standard accretion disc model relies upon several assumptions, the most important of which is geometrical thinness. Whenever this condition is violated, new physical effects become important such as radial energy advection and mass loss from the disc. These effects are important, for instance, for large mass accretion rates when the disc approaches its local Eddington limit. In this work, we study the upper limits for standard accretion disc approximation and find the corrections to the standard model that should be considered in any model aiming on reproducing the transition to super-Eddington accretion regime. First, we find that for thin accretion disc, taking into account relativistic corrections allows to increase the local Eddington limit by about a factor of 2 due to stronger gravity in general relativity (GR). However, violation of the local Eddington limit also means large disc thickness. To consider consequently the disc thickness effects, one should make assumptions upon the two-dimensional rotation law of the disc. For rotation frequency constant on cylinders r sin θ = const, vertical gravity becomes stronger with height on spheres of constant radius. On the other hand, effects of radial flux advection increase the flux density in the inner parts of the disc and lower the Eddington limit. In general, the effects connected to disc thickness tend to increase the local Eddington limit even more. The efficiency of accretion is however decreased by advection effects by about a factor of several.



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