  We investigate three-dimensional relativistic trajectories of test particles
in the spacetime of a slowly rotating compact star, under the combined
influence of gravity and a strong, near-Eddington radiation field. While in the
static case a spherically symmetric shell of matter suspended above the stellar
surface can be formed at the location of radial equilibrium of effective
forces, the same is not true for a rotating star. In the latter case the
symmetry is broken by the interplay between motion in the non-static spacetime
and the influence of strong radiation drag forces, pushing particles towards
the equatorial plane. As a result an expanding spherical shell of matter
ejected from the neutron star surface collapses on a short timescale into a
single stable equatorial ring supported by radiation. These findings have
implications for the geometry of optically thin outflows during luminous
neutron star bursts.
