On accretion disks and metric theories of gravitation

The luminosity of an accretion disk around a compact object is: L=(1-Eo)(dM/dt)c2, with (dM/dt) being the mass per unit time entering the disk and Eo the energy as seen at infinity per rest energy at the last stable circular orbit. This energy and the maximum orbital frequency νm are computed using the most general metric with spherical symmetry. The computations taking some particular metrics, different from the Schwarzschild one, are then carried out to show the dependence of Eo and νm on the theory of gravitation used. Finally the analysis is extended using the most general stationary metric to take into account the rotation of the compac object. (author)