Photon sphere
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Gravitational-wave signatures of exotic compact objects and of quantum corrections at the horizon scale Open
Gravitational waves from binary coalescences provide one of the cleanest signatures of the nature of compact objects. It has been recently argued that the post-merger ringdown waveform of exotic ultracompact objects is initially identical …
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The shape of the black hole photon ring: A precise test of strong-field general relativity Open
We propose a new test of strong-field general relativity (GR) based on the universal interferometric signature of the black hole photon ring. The photon ring is a narrow ring-shaped feature, predicted by GR but not yet observed, that appea…
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Hawking radiation and deflection of light from Rindler modified Schwarzschild black hole Open
We investigate the Hawking radiation of massive spin-1 vector particles,\nwhich are coupled to vacuum fluctuations of a quantum field, from Rindler\nmodified Schwarzschild black hole. Rindler acceleration is used to produce the\npost-gener…
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Shadows and optical appearance of black bounces illuminated by a thin\n accretion disk Open
We study the light rings and shadows of an uniparametric family of\nspherically symmetric geometries interpolating between the Schwarzschild\nsolution, a regular black hole, and a traversable wormhole, and dubbed as black\nbounces, all of …
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Shadows and gravitational weak lensing by the Schwarzschild black hole in the string cloud background with quintessential field* Open
In this study, we observe that, in the presence of the string cloud parameter a and the quintessence parameter γ , with the equation of state parameter , the radius of the shadow of the Schwarzschild black hole increases as compared with t…
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Photon ring and observational appearance of a hairy black hole Open
Recently, the image of a Schwarzschild black hole with an accretion disk has been revisited, and it showed that the "photon ring", defined as highly bent light rays that intersect the disk plane more than twice, is extremely narrow and mak…
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Image of the Janis-Newman-Winicour naked singularity with a thin accretion disk Open
We study the optical appearance and the apparent radiation flux of a thin\naccretion disk around the static Janis-Newman-Winicour naked singularity. We\nconfine ourselves to the astrophysically most relevant case, when the solution\nposses…
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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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Topological charge and black hole photon spheres Open
Black hole photon spheres or light rings are closely linked to astronomical phenomena, such as gravitational waves and the shadow in spherically symmetric or axisymmetric spacetime. In Cunha and Herdciro [Phys. Rev. Lett. 124, 181101 (2020…
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Light curves of light rays passing through a wormhole Open
Gravitational lensing is a good probe into the topological structure of dark\ngravitating celestial objects. In this paper, we investigate the light curve of\na light ray that passes through the throat of an Ellis wormhole, the simplest\ne…
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Photon spheres and sonic horizons in black holes from supergravity and other theories Open
We study closed photon orbits in spherically-symmetric static solutions of supergravity theories, a Horndeski theory, and a theory of quintessence. These orbits lie in what we shall call a photon sphere (anti-photon sphere) if the orbit is…
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Understanding photon sphere and black hole shadow in dynamically evolving spacetimes Open
We have derived the differential equation governing the evolution of the photon sphere for dynamical black hole spacetimes with or without spherical symmetry. Numerical solution of the same depicting evolution of the photon sphere has been…
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A novel gravitational lensing feature by wormholes Open
Horizonless compact objects with light rings (or photon spheres) are becoming\nincreasingly popular in recent years for several reasons. In this paper, we\nshow that a horizonless object such as a wormhole of Morris-Thorne type can\nhave t…
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Photon spheres and spherical accretion image of a hairy black hole Open
In this paper, we first consider null geodesics of a class of charged,\nspherical and asymptotically flat hairy black holes in an\nEinstein-Maxwell-scalar theory with a non-minimal coupling for the scalar and\nelectromagnetic fields. Remar…
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Does the black hole shadow probe the event horizon geometry? Open
There is an exciting prospect of obtaining the shadow of astrophysical black\nholes (BHs) in the near future with the Event Horizon Telescope. As a matter of\nprinciple, this justifies asking how much one can learn about the BH horizon\nit…
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Circular orbit of a particle and weak gravitational lensing Open
The purpose of this paper is twofold. First, we introduce a geometric approach to study the circular orbit of a particle in static and spherically symmetric spacetime based on Jacobi metric. Second, we apply the circular orbit to study the…
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Gravitational lensing by two photon spheres in a black-bounce spacetime\n in strong deflection limits Open
We investigate gravitational lensing by a primary photon sphere which is a\nsphere filled with unstable circular light orbits, and by a secondary photon\nsphere on a wormhole throat in a black-bounce spacetime which is suggested in\n[F. S.…
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Shadow of a naked singularity without photon sphere Open
It is generally believed that the shadows of either a black hole or naked\nsingularity arise due to photon spheres developing in these spacetimes. Here we\npropose a new spherically symmetric naked singularity spacetime solution of\nEinste…
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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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Gravitational lensing in black-bounce spacetimes Open
In this work, we calculate the deflection angle of light in a spacetime that interpolates between regular black holes and traversable wormholes, depending on the free parameter of the metric. Afterwards, this angular deflection is substitu…
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Particle acceleration around rotating Einstein-Born-Infeld black hole and plasma effect on gravitational lensing Open
We consider a time-like geodesics in the background of rotating\nEinstein-Born-Infeld (EBI) black hole to examine the horizon and ergosphere\nstructure. The effective potential that governs the particle's motion in the\nspacetime and the i…
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Charged black hole in 4D Einstein-Gauss-Bonnet gravity: particle motion, plasma effect on weak gravitational lensing and centre-of-mass energy Open
We study the motion of charged and spinning particles and photons in the $4D$\ncharged Einstein-Gauss-Bonnet (EGB) black hole vicinity. We determine the\nradius of the innermost stable circular orbit (ISCO) for test particles. We\nshow tha…
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Quasinormal ringing of regular black holes in asymptotically safe gravity: the importance of overtones Open
Asymptotically safe gravity is based on the idea that the main contribution to the Schwarzschild-like black hole spacetime is due to the value of the gravitational coupling which depends on the distance from the origin and approaches its c…
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Analytical approach to strong gravitational lensing from ultracompact objects Open
Strong gravitational lensing from black holes results in the formation of\nrelativistic images, in particular, relativistic Einstein rings. For objects\nwith event horizons, the radius of the unstable light ring (photon sphere) is\nthe low…
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Shadows and rings of the Kehagias-Sfetsos black hole surrounded by thin disk accretion Open
In this paper, under the illumination of thin disk accretion, we have employed the ray-tracing method to carefully investigate shadows and rings of the Kehagias-Sfetsos(KS) black hole in deformed Hořava-Lifshitz(HL) gravity. The results sh…
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Axion-plasmon or magnetized plasma effect on an observable shadow and gravitational lensing of a Schwarzschild black hole Open
In this paper, we study the influence of the axion-plasmon, as proposed in\n(Phys. Rev. Lett. 120, 181803 (2018)) on the optical properties of the\nSchwarzschild black hole. Our aim is to provide a test to detect the effects of\na fixed ax…
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Exact black hole solutions in shift-symmetric quadratic degenerate higher-order scalar-tensor theories Open
We find various exact black hole solutions in the shift-symmetric subclass of\nthe quadratic degenerate higher-order scalar-tensor (DHOST) theories with\nlinearly time dependent scalar field whose kinetic term is constant. The exact\nsolut…
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Influence of a plasma on the observational signature of a high-spin Kerr black hole Open
To approach a more reliable observational signature of a high-spin Kerr black hole, one should take into account the effects of its surroundings. To this end we study in this paper the influence of a surrounding plasma. We consider its ref…
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Revisiting the shadow of a black hole in the presence of a plasma Open
We study the photon’s motion around a black hole in the presence of a plasma whose density is a function of the radius coordinate by a renewed ray-tracing algorithm and investigate the influence of the plasma on the shadow of the black hol…
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Novel shadows from the asymmetric thin-shell wormhole Open
For dark compact objects such as black holes or wormholes, the shadow size has long been thought to be determined by the unstable photon sphere (region). However, by considering the asymmetric thin-shell wormhole (ATSW) model, we find that…