Radiatively Driven Plasma Jets around Compact Objects

Matter accreting onto black holes may develop shocks due to the centrifugal barrier. A part of inflowing matter in the post-shock flow is deflected along the axis in the form of jets. Post-shock flow which behaves like a Compton cloud has `hot' electrons emiting high energy photons. We study the effect of these `hot' photons on the outflowing matter. Radiation from this region could accelerate the outflowing matter but radiation pressure should also slow it down. We show that the radiation drag restricts the flow from attaining a very high velocity. We introduce the concept of an `equilibrium velocity' ($v_{eq} \sim 0.5c$) which sets the upper limit of the terminal velocity achieved by a cold plasma due to radiation deposition force in the absence of gravity. If the injection energy is $E_{in}$, then we find that the terminal velocity $v_\infty$ satisfies a relation $v_\infty^2 \lsim v_{eq}^2 + 2 E_{in}$.