The vertical structure and stability of accretion disks surrounding black holes and neutron stars

The structure and stability of the inner regions of accretion disks surrounding neutron stars and black holes have been studied. Within the framework of the α viscosity prescription for optically thick disks, we assume the viscous stress scales with gas pressure only, and the α parameter, which is less than or equal to unity, is formulated as α0(h/r)n, where h is the local scale height and n and α0 are constants. We neglect advective energy transport associated with radial motions and construct the vertical disk structures by assuming a Keplerian rotation law and local hydrostatic and thermal equilibrium. The vertical structures have been calculated with and without convective energy transport, and it is found that convection is important especially for mass accretion rates greater than about 0.1 times the Eddington value, MEdd. Although convective efficiency is low, convection does help to stabilize the disk. The results show that the disk can be locally unstable and that for n≳0.75, an S‐shaped relatio...