The apparent shape of a rotating charged black hole, closed photon orbits and the bifurcation set A(4)

The apparent shapes of various Kerr-Newman spacetimes are plotted. For this purpose the geometry of closed photon orbits is studied, forming a subset of the bifurcation set A(4), well known in elementary catastrophe theory. O ne additional result is that the cosmic censorship hypothesis guarantees th at the spacetime casts a shadow, whereas naked ring singularities enable th e visibility of the 'anti-world' of negative radii r through its interior M oreover, the optical restrictions to the observability of the shadow of an astronomical black hole are inferred.