The fingerprints of black holes—shadows and their degeneracies

Mars, Marc; Paganini, Claudio F.; A., Oancea, Marius

doi:10.1088/1361-6382/aa97ff

Cited by 41 publications

(24 citation statements)

References 27 publications

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“…Various related investigations have been carried out by many groups (e.g. [6][7][8][9][10][11][12][13][14][15][16][17]). Although the velocity of the observer can yield aberrational effects, these were found to be negligible for observing the shadow of Sgr A* [18].…”

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confidence: 99%

Intrinsic curvature and topology of shadows in Kerr spacetime

2019

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From the viewpoint of differential geometry and topology, we investigate the characterization of the shadows in a Kerr spacetime. Two new quantities, the length of the shadow boundary and the local curvature radius are introduced. Each shadow can be uniquely determined by these two quantities. For the black hole case, the result shows that we can constrain the black hole spin and the angular coordinate of the observer by only measuring the maximum and minimum of the curvature radius. While for the naked singularity case, we adopt the length parameter and the maximum of the curvature radius. This technique is completely independent of the coordinate system and the location of the shadow, and is expected to uniquely determine the parameters of the spacetime. Moreover, we propose a topological covariant quantity to measure and distinguish different topological structures of the shadows.

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confidence: 99%

Intrinsic curvature and topology of shadows in Kerr spacetime

2019

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“…Because we do not a priori know the distance between Earth and an observed astrophysical black hole we cannot lift this degeneracy using observations of the shadow alone. Mars, Paganini and Oancea [47] showed that for Kerr-Newman black holes and observer's that are not located on the axis of symmetry this degeneracy is lifted. They also concluded that for Kerr-Newman-NUT black holes the only parameter that cannot be determined from observations of the shadow alone is the gravitomagnetic charge n. However, in this paper we do not consider the spin and therefore we need additional observables that help us to distinguish between the shadows in different spacetimes and to potentially measure the gravitomagnetic charge n.…”

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confidence: 99%

Gravitational Lensing in the Charged NUT-de Sitter Spacetime

Frost

2021

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“…In practice, however, the light emitting astrophysical environment around the BH may cause degeneracies and make very different spacetimes potentially yield similar shadows -see e.g. [21,22] for examples.…”

Section: Introductionmentioning

confidence: 99%

Does the black hole shadow probe the event horizon geometry?

2018

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There is an exciting prospect of obtaining the shadow of astrophysical black holes (BHs) in the near future with the Event Horizon Telescope. As a matter of principle, this justifies asking how much one can learn about the BH horizon itself from such a measurement. Since the shadow is determined by a set of special photon orbits, rather than horizon properties, it is possible that different horizon geometries yield similar shadows. One may then ask how sensitive is the shadow to details of the horizon geometry? As a case study, we consider the double Schwarzschild BH and analyse the impact on the lensing and shadows of the conical singularity that holds the two BHs in equilibrium -herein taken to be a strut along the symmetry axis in between the two BHs. Whereas the conical singularity induces a discontinuity of the scattering angle of photons, clearly visible in the lensing patterns along the direction of the strut's location, it produces no observable effect on the shadows, whose edges remain everywhere smooth. The latter feature is illustrated by examples including both equal and unequal mass BHs. This smoothness contrasts with the intrinsic geometry of the (spatial sections of the) horizon of these BHs, which is not smooth, and provides a sharp example on how BH shadows are insensitive to some horizon geometry details. This observation, moreover, suggests that for the study of their shadows, this static double BH system may be an informative proxy for a dynamical binary.

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The fingerprints of black holes—shadows and their degeneracies

Cited by 41 publications

References 27 publications

Intrinsic curvature and topology of shadows in Kerr spacetime

Intrinsic curvature and topology of shadows in Kerr spacetime

Gravitational Lensing in the Charged NUT-de Sitter Spacetime

Does the black hole shadow probe the event horizon geometry?

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