Line-driven winds in presence of strong gravitational fields

Abstract

We propose a general physical mechanism which could contribute to the formation of fast line-driven outflows at the vicinity of strong gravitational field sources. We argue that the gradient of the gravitational potential plays the same role as the velocity gradient plays in Sobolev approximation. Both Doppler effect and gravitational redshifting are taken into account in Sobolev approximation. The radiation force becomes a function of the local velocity gradient and the gradient of the gravitational potential. The derived equation of motion has a critical point that is different from that of CAK. A solution that is continuous through the singular point is obtained numerically. A comparison with CAK theory is presented. It is shown that the developed theory predicts terminal velocities which are greater than those obtained from the CAK theory.