A recipe for making hot accretion disks

A powerful new method to determine the structure of effectively optically thin accretion disks (even when complicated microphysics is included) has been discovered. The method reduces the set of equations that needs to be solved numerically to the microphysical equations only. Furthermore, the method reduces the dimension of the parameter space that needs to be explored from three (accretion rate, viscosity, radius) to two ("proton optical depth," τ_p, and compactness, l) significantly reducing the computational effort. The method contains two steps. First, the equilibrium states of hot plasma clouds (HPCs) are determined as a function of τ_p and l by solving the microphysical equations. Then the disk structure equations are solved analytically giving two relations between the HPC parameters, τ_p and l, and two accretion disk parameters. The two relations map the computed equilibrium states into the accretion disk parameter space. The disk structure for τ_p or l for all applicable accretion rates, viscosities, and radii can conveniently be visualized in one single figure. As a tutorial example, disk structures are constructed for effectively optically thin brems-strahlung disks.