Discrete degeneracies of Kerr–Newman shadow contours

Determine whether distinct Kerr–Newman black-hole parameter sets can produce congruent full shadow contours for observers viewing the black hole away from its symmetry axis, thereby resolving the possible discrete degeneracies left after continuous degeneracies have been excluded.

Background

The paper situates its Kerr critical-curve uniqueness result within earlier work on black-hole shadow degeneracies. For Kerr–Newman black holes observed away from the symmetry axis, continuous degeneracies of shadow contours had been ruled out, but the cited analysis had not resolved whether distinct parameter sets might nevertheless yield identical contours through a discrete degeneracy. This unresolved issue concerns full shadow contours rather than the positive-length Kerr critical-curve segments treated by the present paper.