1. J.M. Bardeen, Timelike and null geodesics in the Kerr metric, in Black Holes, ed. by C. Dewitt, B.S. Dewitt (Gordon and Breach, New York, 1973), pp. 215–239
2. P. Nedkova, V. Tinchev, S. Yazadjiev, Shadow of a rotating traversable wormhole. Phys. Rev. D 88, 124019 (2013)
3. N. Sakai, H. Saida, T. Tamaki, Gravastar shadows. Phys. Rev. D 90, 104013 (2014)
4. P. Cunha, C. Herdeiro, M.J. Rodriguez, Does the black hole shadow probe the event horizon geometry? Phys. Rev. D 97, 084020 (2018)
5. S. Doeleman, E. Agol, D. Backer et al., Imaging an event horizon: submm-VLBI of a super massive black hole, Astro2010: The Astronomy and Astrophysics Decadal Survey, Science White Papers, No. 68 (2009)