Kerr metric ≈ Kerr metric
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First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring Open
The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider the physical implications of the asymmetric ring seen in the 2017 …
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New method for shadow calculations: Application to parametrized axisymmetric black holes Open
Collaborative international efforts under the name of the Event Horizon\nTelescope project, using sub- mm very long baseline interferometry, are soon\nexpected to provide the first images of the shadow cast by the candidate\nsupermassive b…
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General parametrization of axisymmetric black holes in metric theories of gravity Open
Following previous work of ours in spherical symmetry, we here propose a new\nparametric framework to describe the spacetime of axisymmetric black holes in\ngeneric metric theories of gravity. In this case, the metric components are\nfunct…
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Parameter estimation of hairy Kerr black holes from its shadow and constraints from M87* Open
The recently obtained hairy Kerr black holes, due to additional sources or surrounding fluid, like dark matter, with conserved energy-momentum tensor, have a deviation α and primary hair l0, apart from rotation parameter a and mass M. In t…
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The linear stability of the Schwarzschild solution to gravitational perturbations Open
We prove in this paper the linear stability of the celebrated Schwarzschild family of black holes in general relativity: Solutions to the linearisation of the Einstein vacuum equations around a Schwarzschild metric arising from regular ini…
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Testing the Kerr Black Hole Hypothesis Using X-Ray Reflection Spectroscopy Open
We present the first X-ray reflection model for testing the assumption that the metric of astrophysical black holes is described by the Kerr solution. We employ the formalism of the transfer function proposed by Cunningham. The calculation…
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Tidal Love numbers of Kerr black holes Open
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Static response and Love numbers of Schwarzschild black holes Open
We derive the quadratic action for the physical degrees of freedom of massless spin-0, spin-1, and spin-2 perturbations on a Schwarzschild-(A)dS background in arbitrary dimensions. We then use these results to compute the static response o…
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Can different black holes cast the same shadow? Open
We consider the following question: may two different black holes (BHs) cast exactly the same shadow? In spherical symmetry, we show the necessary and sufficient condition for a static BH to be shadow-degenerate with Schwarzschild is that …
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No-hair theorem in the wake of Event Horizon Telescope Open
Thanks to the release of the extraordinary EHT image of shadow attributed to the M87* supermassive black hole (SMBH), we have a novel window to assess the validity of fundamental physics in the strong-field regime. Motivated by this, we co…
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Astrophysical imaging of Kerr black holes with scalar hair Open
We address the astrophysical imaging of a family of deformed Kerr black holes\n(BHs). These are stationary, asymptotically flat black hole (BH) spacetimes,\nthat are solutions of General Relativity minimally coupled to a massive,\ncomplex …
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Distinguishing Fuzzballs from Black Holes through Their Multipolar Structure Open
Within general relativity, the unique stationary solution of an isolated black hole is the Kerr spacetime, which has a peculiar multipolar structure depending only on its mass and spin. We develop a general method to extract the multipole …
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Testing General Relativity with the Reflection Spectrum of the Supermassive Black Hole in 1H0707-495 Open
Recently, we have extended the x-ray reflection model relxill to test the spacetime metric in the strong gravitational field of astrophysical black holes. In the present Letter, we employ this extended model to analyze XMM-Newton, NuSTAR, …
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Constraining alternatives to the Kerr black hole Open
The recent observation of the shadow of the supermassive compact object M87* by the Event Horizon Telescope (EHT) collaboration has opened up a new window to probe the strong gravity regime. In this paper, we study shadows cast by two viab…
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Photon rings of spherically symmetric black holes and robust tests of non-Kerr metrics Open
Under very general assumptions on the accretion flow geometry, images of a black hole illuminated by electromagnetic radiation display a sequence of photon rings (demagnified and rotated copies of the direct image) which asymptotically app…
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Testing Horndeski Gravity from EHT Observational Results for Rotating Black Holes Open
The Event Horizon Telescope (EHT) collaboration recently unveiled the first image of the supermassive black hole M87*, which exhibited a ring of angular diameter θ d = 42 ± 3 μ as, a circularity deviation of Δ C ≤ 0.1, and also inferred a …
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Rotating regular black holes in conformal massive gravity Open
In this paper, we use a suitable conformal rescaling to construct static and rotating regular black holes in conformal massive gravity. The new metric is characterized by the mass $M$, the "scalar charge" $Q$, the angular momentum paramete…
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Penrose Process: Its Variants and Astrophysical Applications Open
We present a review of the Penrose process and its modifications in relation to the Kerr black holes and naked singularities (superspinars). We introduce the standard variant of this process, its magnetic version connected with magnetized …
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Numerical computation of second-order vacuum perturbations of Kerr black holes Open
Motivated by the desire to understand the leading order nonlinear\ngravitational wave interactions around arbitrarily rapidly rotating Kerr black\nholes, we describe a numerical code designed to compute second order vacuum\nperturbations o…
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Black hole merger estimates in Einstein-Maxwell and Einstein-Maxwell-dilaton gravity Open
The recent birth of gravitational wave astronomy invites a new generation of precision tests of general relativity. Signatures of black hole (BH) mergers must be systematically explored in a wide spectrum of modified gravity theories. Here…
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Public Release of RELXILL_NK: A Relativistic Reflection Model for Testing Einstein’s Gravity Open
We present the public release version of relxill _ nk , an X-ray reflection model for testing the Kerr hypothesis and general relativity. This model extends the relxill model that assumes the black hole (BH) spacetime is described by the K…
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Black hole shadow as a test of general relativity: quadratic gravity Open
Observations of the black hole shadow of supermassive black holes, such as\nSagittarius A* at the center of our Milky Way galaxy, allow us to study the\nproperties of black holes and the nature of strong-field gravity. According to\nthe Ke…
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Timelike geodesics in naked singularity and black hole spacetimes Open
In this paper, we derive the solutions of orbit equations for a class of\nnaked singularity spacetimes, and compare these with timelike orbits, that is,\nparticle trajectories in the Schwarzschild black hole spacetime. The\nSchwarzschild a…
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Post-Kerr black hole spectroscopy Open
One of the central goals of the newborn field of gravitational wave astronomy is to test gravity in the highly nonlinear, strong field regime characterizing the spacetime of black holes. In particular, "black hole spectroscopy" (the observ…
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Shadow of axisymmetric, stationary and asymptotically flat black holes in the presence of plasma Open
We study the shadow produced by a class of rotating black holes surrounded by plasma. The metric for these black holes arises by applying the Newman-Janis algorithm to a family of spherically symmetric spacetimes, which includes several we…
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Imaging a non-singular rotating black hole at the center of the Galaxy Open
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Black Hole Images as Tests of General Relativity: Effects of Spacetime Geometry Open
The images of supermassive black holes surrounded by optically thin, radiatively inefficient accretion flows, like those observed with the Event Horizon Telescope, are characterized by a bright ring of emission surrounding the black hole s…
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Axisymmetric black holes allowing for separation of variables in the Klein-Gordon and Hamilton-Jacobi equations Open
We determine the class of axisymmetric and asymptotically flat black-hole\nspacetimes for which the test Klein-Gordon and Hamilton-Jacobi equations allow\nfor the separation of variables. The known Kerr, Kerr-Newman, Kerr-Sen and some\noth…
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Quasibound states of Schwarzschild acoustic black holes Open
In this paper, we study the recently proposed Schwarzschild acoustic black\nhole spacetime, in which we investigate some physical phenomena related to the\neffective geometry of this background, including the analogous Hawking\nradiation a…
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Completion of metric reconstruction for a particle orbiting a Kerr black hole Open
Vacuum perturbations of the Kerr metric can be reconstructed from the\ncorresponding perturbation in either of the two Weyl scalars $\\psi_0$ or\n$\\psi_4$, using a procedure described by Chrzanowski and others in the 1970s.\nMore recent w…