Particles under radiation thrust in Schwarzschild space-time from a flux perpendicular to the equatorial plane

TL;DR

This study models the motion of particles under radiation thrust in Schwarzschild space-time, showing how radiation influences particle collimation and acceleration perpendicular to a black hole's accretion disc.

Contribution

It introduces a new model of particle-radiation interaction in Schwarzschild space-time considering a perpendicular radiation flux from an accretion disc.

Findings

Particles are strongly influenced by radiation flux

Particles are collimated and accelerated perpendicular to the disc

Radiation acceleration alone cannot produce highly relativistic outflows

Abstract

Motivated by the picture of a thin accretion disc around a black hole, radiating mainly in the direction perpendicular to its plane, we study the motion of test particles interacting with a test geodesic radiation flux originating in the equatorial plane of a Schwarzschild space-time and propagating initially in the perpendicular direction. We assume that the interaction with the test particles is modelled by an effective term corresponding to the Thomson-type interaction which governs the Poynting-Robertson effect. After approximating the individual photon trajectories adequately, we solve the continuity equation approximately in order to find a consistent flux density with a certain plausible prescribed equatorial profile. The combined effects of gravity and radiation are illustrated in several typical figures which confirm that the particles are generically strongly influenced by the flux. In particular, they are both collimated and accelerated in the direction perpendicular to the disc, but this acceleration is not enough to explain highly relativistic outflows emanating from some black hole-disc sources. The model can however be improved in a number of ways before posing further questions which are summarized in concluding remarks.