Black hole shadow in an asymptotically flat, stationary, and axisymmetric spacetime: The Kerr-Newman and rotating regular black holes

Tsukamoto, Naoki

doi:10.1103/physrevd.97.064021

Cited by 173 publications

(91 citation statements)

References 85 publications

(57 reference statements)

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“…In this work, we study shadow cast by a general rotating black hole generated from a nonrotating one through the NJ algorithm. A similar work has been considered in [95] in the case when the initial nonrotating seed black hole spacetime has a particular ansatz. However, our work here is not restricted to such an ansatz and deals with a most general rotating black hole generated through the NJ algorithm.…”

Section: Introductionmentioning

confidence: 91%

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Black hole shadow in a general rotating spacetime obtained through Newman-Janis algorithm

2019

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The Newman-Janis (NJ) algorithm has been extensively used in the literature to generate rotating black hole solutions from nonrotating seed spacetimes. In this work, we show, using various constants of motion, that the null geodesic equations in an arbitrary stationary and axially symmetric rotating spacetime obtained through the NJ algorithm can be separated completely, provided that the algorithm is applied successfully without any inconsistency.Using the separated null geodesic equations, we then obtain an analytic general formula for obtaining the contour of a shadow cast by a compact object whose gravitational field is given by the arbitrary rotating spacetime under consideration. As special cases, we apply our general analytic formula to some known black holes and reproduce the corresponding results for black hole shadow. Finally, we consider a new example and study shadow using our analytic general formula. * rshaikh@iitk.ac.in

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Section: Introductionmentioning

confidence: 91%

“…has been considered in [95]. In this case, using (16), the metric functions can be complexified to obtain [92]…”

Section: Separation Of Null Geodesic Equations and Black Hole Shmentioning

confidence: 99%

Black hole shadow in a general rotating spacetime obtained through Newman-Janis algorithm

2019

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“…Further, the shadows of super-extremal Kerr black holes [16] and Kerr-Newman-NUT spacetimes [83] as well as Kerr black holes with scalar hair [46,142] have been explored. Regular spacetimes have been studied in [3,9,133,138]. The shadow of non-commutative-geometry inspired black-hole spacetimes has been investigated in [147].…”

Section: Motivationmentioning

confidence: 99%

Asymptotic safety casts its shadow

Held

Gold

Eichhorn

2019

J. Cosmol. Astropart. Phys.

113

138

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We set out to bridge the gap between regular black-hole spacetimes and observations of a black-hole shadow by the Event Horizon Telescope. We explore modifications of spinning and non-spinning black-hole spacetimes inspired by asymptotically safe quantum gravity which features a scale dependence of the Newton coupling. As a consequence, the predictions of our model, such as the shadow shape and size, depend on one free parameter determining the curvature scale at which deviations from General Relativity set in. In more general new-physics settings, it can also depart substantially from the Planck scale. In this case, the free parameter is constrained by observations, since the corresponding curvature scale is significantly below the Planck-scale. The leading new-physics effect can be recast as a scale-dependent black-hole mass, resulting in distinct observational signatures of our model. As a concrete example, we show that two mass-measurements, extracted from the size of the shadow and from Keplerian orbital motion of stars, allow to distinguish the classical from the modified, regular black-hole spacetime, yielding a bound on the free parameter. For spinning black holes, we further find that the singularity-resolving new physics puts a characteristic dent in the shadow. Finally, we argue, based on the underlying physical mechanism, that the effects we derive could be generic consequences of a large class of quantum-gravity theories.

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“…More recently, the shadows of many others rotating black hole solutions have been investigated, including, e.g. of Kerr-Newman black holes [33,34], Kerr black holes with scalar hair [35][36][37], Kerr-Sen [38], spontaneously scalarised Kerr black holes [39], Kaluza-Klein dyonic rotating black holes [40], the double Kerr solution [41], spinning Einstein-Maxwell dilaton black holes [42] and rotating regular black holes [34].…”

Section: Introductionmentioning

confidence: 99%

Spinning black holes with a separable Hamilton–Jacobi equation from a modified Newman–Janis algorithm

et al. 2020

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Obtaining solutions of the Einstein field equations describing spinning compact bodies is typically challenging. The Newman–Janis algorithm provides a procedure to obtain rotating spacetimes from a static, spherically symmetric, seed metric. It is not guaranteed, however, that the resulting rotating spacetime solves the same field equations as the seed. Moreover, the former may not be circular, and thus expressible in Boyer–Lindquist-like coordinates. Amongst the variations of the original procedure, a modified Newman–Janis algorithm (MNJA) has been proposed that, by construction, originates a circular, spinning spacetime, expressible in Boyer–Lindquist-like coordinates. As a down side, the procedure introduces an ambiguity, that requires extra assumptions on the matter content of the model. In this paper we observe that the rotating spacetimes obtained through the MNJA always admit separability of the Hamilton–Jacobi equation for the case of null geodesics, in which case, moreover, the aforementioned ambiguity has no impact, since it amounts to an overall metric conformal factor. We also show that the Hamilton–Jacobi equation for light rays propagating in a plasma admits separability if the plasma frequency obeys a certain constraint. As an illustration, we compute the shadow and lensing of some spinning black holes obtained by the MNJA.

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Black hole shadow in an asymptotically flat, stationary, and axisymmetric spacetime: The Kerr-Newman and rotating regular black holes

Cited by 173 publications

References 85 publications

Black hole shadow in a general rotating spacetime obtained through Newman-Janis algorithm

Black hole shadow in a general rotating spacetime obtained through Newman-Janis algorithm

Asymptotic safety casts its shadow

Spinning black holes with a separable Hamilton–Jacobi equation from a modified Newman–Janis algorithm

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