TWO-DIMENSIONAL NUMERICAL SIMULATIONS OF SUPERCRITICAL ACCRETION FLOWS REVISITED

Abstract

We study the dynamics of super-Eddington accretion flows by performing\ntwo-dimensional radiation-hydrodynamic simulations. Compared with previous\nworks, in this paper we include the $T_{\\theta\\phi}$ component of the viscous\nstress and consider various values of the viscous parameter $\\alpha$. We find\nthat when $T_{\\theta\\phi}$ is included, the rotational speed of the\nhigh-latitude flow decreases, while the density increases and decreases at the\nhigh and low latitudes, respectively. We calculate the radial profiles of\ninflow and outflow rates. We find that the inflow rate decreases inward,\nfollowing a power law form of $\\dot{M}_{\\rm in}\\propto r^s$. The value of $s$\ndepends on the magnitude of $\\alpha$ and is within the range of $\\sim 0.4-1.0$.\nCorrespondingly, the radial profile of density becomes flatter compared with\nthe case of a constant $\\dot{M}(r)$. We find that the density profile can be\ndescribed by $\\rho(r)\\propto r^{-p}$, and the value of $p$ is almost same for a\nwide range of $\\alpha$ ranging from $\\alpha=0.1$ to $0.005$. The inward\ndecrease of inflow accretion rate is very similar to hot accretion flows, which\nis attributed to the mass loss in outflows. To study the origin of outflow, we\nanalyze the convective stability of slim disk. We find that depending on the\nvalue of $\\alpha$, the flow is marginally stable (when $\\alpha$ is small) or\nunstable (when $\\alpha$ is large). This is different from the case of\nhydrodynamical hot accretion flow where radiation is dynamically unimportant\nand the flow is always convectively unstable. We speculate that the reason for\nthe difference is because radiation can stabilize convection. The origin of\noutflow is thus likely because of the joint function of convection and\nradiation, but further investigation is required.\n