Motion of accreting matter near luminous slowly rotating relativistic stars

In a previous paper, we reported test particle calculations showing that the behavior of accretion flows near uniformly emitting, nonrotating, relativistic stars is affected significantly by radiation forces if the luminosity is greater than similar to 1% of the Eddington critical luminosity L(E). Here, using a numerical code that can follow the motion of a test particle in any stationary axisymmetric spacetime, we investigate the effects of nonuniform emission and of slow rotation of the gravitating mass and radiation source, when their rotation axes are co-aligned. We find that for emission from a bright, thin ring, accreting particles are braked sharply near the radiation source, which may be favorable for the development of shock waves. We also show that if the particle orbit is prograde with respect to the rotation of the radiation source, the rates at which energy and angular momentum are lost to the radiation held are less than the rates for a nonrotating source. The diminished loss rates lead to a lower inward radial velocity, which increases the infall time. Surprisingly, if the radiation flux is sufficiently small, the increase in the infall time more than compensates for the decrease in the loss rates, so the total energy and angular momentum transferred to the radiation held during particle inspiral are actually greater than for a nonrotating radiation source. We also discuss some of the effects of radiation forces on accreting fluid. We show that the angular, special relativistic, and general relativistic effects that augment radiation drag on test particles near radiating relativistic stars also increase the fraction of angular momentum and energy that can be transferred from the accretion flow to the radiation field. This may affect the maximum rotation rate of neutron stars and the prospects for observing gravitational radiation from rapidly rotating neutron stars.