Radiative acceleration in Schwarzschild space-times

We examine the radial motion of a material particle in the intense radiatio n field of a static spherically symmetric compact object with spherical emi tting surface outside the Schwarzschild radius. This paper generalizes prev ious work which dealt with radial motion in the Thomson limit, where the ra diation force is simply proportional to the radiative flux. In the general case the average time component of the 4-momentum transferred to the partic le is not negligible compared with its rest mass. Consequently, we find tha t the frequency dependence of the radiation force owing to Compton scatteri ng for highly energetic photons gives rise to an increase in the effective mass of the test particle. In this work we outline the effects of this freq uency dependence and compare these with the results in the Thomson limit. W e present the frequency dependent saturation velocity curves for a range of stellar luminosities and radiation frequencies and present the resulting p hase-space diagrams corresponding to the radial test particle trajectories. In particular, the stable equilibrium points which exist in the Thomson li mit are found to be absent in the general case.