Trapping of null geodesics in slowly rotating spacetimes Jaroslav Vrba, Martin Urbanec, Zdeněk Stuchlík and John C. Miller Eur. Phys. J. C, 80 11 (2020) 1065 Published online: 19 November 2020 DOI: 10.1140/epjc/s10052-020-08642-z