Particle dynamics on test papapetrou fields of vacuum spacetimes

In this paper we examine the dynamics of test particles subjected to Papapetrou fields which emerge from vacuum spacetimes isometries. Assuming that the background geometry is described by a Kerr metric whose timelike Killing vector satisfies Maxwell equations, we evaluate the electromagnetic fields-Papapetrou fields-by fixing a locally non-rotating (LNR) frame of reference. We also evaluate such the electromagnetic fields for a vanishing rotation parameter assuming a timelike frame of reference for a Schwarzschild background. In order to probe for the effect of the test Papapetrou fields we study the motion of charged particles in a Kerr background. Restricting ourselves to orbits in the equatorial plane with LNR initial conditions we show that there is an explicit deviation between orbits of neutral and charged particles in the case of repulsive electromagnetic configurations. For critical charge-mass ratios zeta * test particles can be found in the Kerr retrograde photon sphere. For static configurations we show that massive/charged test particles may populate the unstable Schwarzschild photon sphere for given domain of the parameter space.