Is the standard accretion disc model invulnerable?

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Abstract
Two-dimensional hydrodynamic calculations of a gas flow in a semi-detached close binary system with mass ratio unity are carried out again, using a different coordinate system from our previous work (Sawada, Matsuda & Hachisu). The Euler equation is solved using the second-order Osher scheme in a multi-box type of grid, which gives a high resolution about a mass-accreting compact object. Spiral-shaped shock waves in the accretion disc are found to extend down to r=0.01A , where r and A are the radial distance from the compact star and the separation of two stars respectively. It means that the tidal effect by the mass-losing star is important even so close to the compact object. It is also confirmed that the gas particles lose their angular momentum at the shocks and can spiral in without the help of a turbulent viscosity. The fundamental assumptions of the standard accretion disc model, i.e. an axisymmetric thin disc, the important role of the turbulent viscosity etc., are questioned.

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