Advection-Dominated Accretion Disks: Geometrically Slim or Thick?

Abstract We revisit the vertical structure of black-hole accretion disks in spherical coordinates. By comparing the advective cooling with the viscous heating, we show that advection-dominated disks are geometrically thick, i.e., with a half-opening angle of $\Delta\theta$$>$ 2$\pi/$5, rather than being slim, as supposed previously in the literature.