Accretion disk equilibria at a particular radial location R = 5r_S and for a black hole mass 10 M_⊙. Flows above the dotted lines τ = 1 are optically thin. The solid S-shaped line on the right represents the optically thick disks, the solid line on the left represents the optically thin disks. The upper branches of both lines represent advection-dominated disks (slim and ADAFs). The Shakura-Sunyaev viscosity parameter is assumed to be α = 0.1. We note the location of the PDs. This figure is adopted (with some simplifications) from Lasota (2015), the original appeared in Abramowicz et al. (1995).