Shadows of spherically symmetric black holes and naked singularities

By R. Shaikh, Prashant Kocherlakota, Ramesh Narayan, P. Joshi. Monthly notices of the Royal Astronomical Society, 2018

260 citations recorded by the source corpus.

We compare shadows cast by Schwarzschild black holes with those produced by two classes of naked singularities that result from gravitational collapse of spherically symmetric matter. The latter models consist of an interior naked singularity space–time restricted to radii r ≤ R_b, matched to Schwarzschild space–time outside the boundary radius R_b. While a black hole always has a photon sphere and always casts a shadow, we find that the naked singularity models have photon spheres only if a certain parameter M_0 that characterizes these models satisfies M_0 ≥ 2/3, or equivalently, if R_b ≤ 3M, where M is the total mass of the object. Such models do produce shadows. However, models with M_0 3M) have no photon sphere and do not produce a shadow. Instead, they produce an interesting ‘full-moon’ image. These results imply that the presence of a shadow does not by itself prove that a compact object is necessarily a black hole. The object could be a naked singularity with M_0 ≥ 2/3, and we will need other observational clues to distinguish the two possibilities. On the other hand, the presence of a full-moon image would certainly rule out a black hole and might suggest a naked singularity with M_0 < 2/3. It would be worthwhile to generalize the present study, which is restricted to spherically symmetric models, to rotating black holes and naked singularities.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/b6fb69e9dc815f9b4937c87d3e5bc8527969005e

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Citations in the corpus

Constraints on black-hole charges with the 2017 EHT observations of M87* (2021, background): “This shadow— which can obviously be associated with black holes [52– 57], but also more exotic compact objects such as gravastars [58,59] or naked singularities [60,61]—is determined entirely by the underlying spacetime metric.”
Shadows and deflection angle of charged and slowly rotating black holes in Einstein-Æther theory (2019, background): “Some notable results of black hole shadows are already discussed in the literature, to list a few: Schwarzschild black hole surrounded by a Bach-Weyl ring [7]; Einstein-dilaton-Gauss-Bonnet black hole [8]; Konoplya-Zhidenko or more general parameterized black holes [9, 10]; Einstein-Maxwell-ChernSim”
Influence of quintessence dark energy on the shadow of black hole (2020, background): “So far, the study of shadows of black holes has become a subject of great interest [12–39].”
Phenomenological aspects of black holes beyond general relativity (2018, unknown): “[148] Rajibul Shaikh, Prashant Kocherlakota, Ramesh”