Thin accretion disks are stabilized by a strong magnetic field

By studying three-dimensional, radiative, global simulations of sub-Eddington, geometrically thin black hole accretion flows we show that thin disks which are dominated by magnetic pressure are stable against thermal instability. Such disks are thicker than predicted by the standard model and show significant amount of dissipation inside the marginally stable orbit. Radiation released in this region, however, does not escape to infinity but is advected into the black hole. We find that the resulting accretion efficiency ($5.5\pm0.5\%$ for the simulated $0.8\dot M_{\rm Edd}$ disk) is very close to the predicted by the standard model ($5.7\%$).