Effects of radiation pressure from resonance scattering in a quasar cloud

The suggestion that those absorption-line systems in quasi-stellar objects for which Ze are caused by the acceleration of clouds by radiation pressure is investigated. The transfer of resonance-line radiation in a static cloud has been solved in order to determine the distribution of the force within the cloud due to radiation pressure. It is shown that radiation pressure will accelerate a discrete cloud coherently only under a restrictive range of conditions. Specifically, if the continuum radiation incident upon a cloud ultimately causes appreciable photon creation within the cloud, e.g., through ionization, the gas will tend to be disrupted by the outward diffusion of the internally created photons as it is accelerated. The conditions which are expected to prevail in the line-emitting regions of QSOs are such that line creation does produce a strong differential expansion if radiation pressure is the predominant force.