Trajectories of zero rest-mass particles and gravitational trapping in interior geometries

Trajectories of zero rest-mass particles (ZRP) are quite well studied in Schwarzschild geometry but not in interior geometries. In this paper the trajectories of ZRP have been obtained and discussed for Tolman's IV solution. It is found that the inward moving ZRP approaches the centre up to a minimum distance and then draws away from it if the angle of emittance is less than that for the cone of avoidance. If, however, the angle of emittance is greater than the angle of cone of avoidance, the ZRP moves inwards up to a certain minimum distance from the centre and then stays at this distance in a circular orbit. In this regard four different kinds of orbits have been identified. Calculations have also been done for the number of ZRP that will escape such massive configuration.