Gravitational lensing by black holes and their alternatives

2017 ◽  
Vol 26 (05) ◽  
pp. 1741013 ◽  
Author(s):  
Valerio Bozza
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Infinite Number ◽  
Gravitational Lensing ◽  
Exotic Matter ◽  
Asymptotic Limit ◽  
Light Rays ◽  
Alternative Solutions

Black holes have the ability to generate infinite number of images of any given source. These relativistic images are formed by light rays winding around the black hole several times. The phenomenology associated with these images is very rich, since these features are very sensitive to the metric structure of the black hole. Here, we review some aspects of gravitational lensing by black holes and consider some fundamental aspects related to alternative solutions, which do not reproduce Schwarzschild in the asymptotic limit and are supported by exotic matter.

scholarly journals Weak Deflection Angle of some Classes of non-linear Electrodynamics Black Holes via Gauss-Bonnet Theorem

2020 ◽  
Author(s):  
Hasan El Moumni ◽  
Karima Masmar ◽  
Ali Övgün
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Lensing ◽  
Deflection Angle ◽  
Weak Field ◽  
Leading Order ◽  
Plasma Medium ◽  
Non Linear ◽  
The Deflection Angle ◽  
Bonnet Theorem

In this paper, we study the gravitational lensing by some black hole classes within the non-linear electrodynamics in weak field limits. First, we calculate an optical geometry of the non-linear electrodynamics black hole then we use the Gauss-Bonnet theorem for finding deflection angle in weak field limits. The effect of non-linear electrodynamics on the deflection angle in leading order terms is studied. Furthermore, we discuss the effects of the plasma medium on the weak deflection angle.

scholarly journals GRAVITATIONAL LENSING IN THE WEAK FIELD LIMIT BY A BRANEWORLD BLACK HOLE

2005 ◽  
Vol 20 (32) ◽  
pp. 2487-2496 ◽  
Author(s):  
A. S. MAJUMDAR ◽  
NUPUR MUKHERJEE
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Lensing ◽  
Cosmic Ray ◽  
Weak Field ◽  
High Energy ◽  
High Energy Particle ◽  
Field Limit ◽  
Weak Field Limit ◽  
Point Light

The existence of braneworld black holes may be of primordial origin, or may even be produced in high energy particle collisions in the laboratory and in cosmic ray showers as well. These black holes obey a modified mass–radius relationship compared to standard Schwarzschild black holes. Using the variational principle we calculate the bending angle of a light ray near the horizon of a braneworld black hole in the weak field limit. We next derive the expressions of several lensing quantities like the Einstein radius and the magnification for a point light source. These expressions are modified compared to the lensing quantities for standard Schwarzschild black holes and contain the scale of the extra dimensions.

Black hole fusion made easy

2016 ◽  
Vol 25 (12) ◽  
pp. 1644015
Author(s):  
Roberto Emparan ◽  
Marina Martínez
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Black Hole ◽  
Event Horizon ◽  
Critical Behavior ◽  
Equivalence Principle ◽  
The Other ◽  
Schwarzschild Solution ◽  
Null Geodesics ◽  
Light Rays

The fusion of two black holes — a signature phenomenon of General Relativity — is usually regarded as a process so complex that nothing short of a supercomputer simulation can accurately capture it. In this essay, we explain how the event horizon of the merger can be found in an exact analytic way in the limit where one of the black holes is much smaller than the other. Remarkably, the ideas and techniques involved are elementary: the equivalence principle, null geodesics in the Schwarzschild solution, and the notion of event horizon itself. With these, one can identify features such as the line of caustics at which light rays enter the horizon, and find indications of universal critical behavior when the two black holes touch.

scholarly journals Gravitational Lensing and Wormhole Shadows

2021 ◽  
Vol 65 (12) ◽  
pp. 1185-1193
Author(s):  
M. A. Bugaev ◽  
I. D. Novikov ◽  
S. V. Repin ◽  
A. A. Shelkovnikova
Keyword(s):  
Black Hole ◽  
Gravitational Lensing ◽  
Formation Process ◽  
Gravitational Mass ◽  
Schwarzschild Black Hole ◽  
Scattering Of Light ◽  
Light Rays

Abstract The problem of bending and scattering of light rays passing outside the entrance of a wormhole with zero gravitational mass is considered. The process of ray capture by a wormhole, as well as the formation process of a shadow when illuminated by a standard screen, is investigated. These mechanisms are also compared to the case of light ray motion in the vicinity of the Schwarzschild black hole.

scholarly journals Study of black hole as dissipative structure using negentropy

2016 ◽  
Vol 94 (10) ◽  
pp. 960-966
Author(s):  
Shripad P. Mahulikar ◽  
Pallavi Rastogi
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Theoretical Investigation ◽  
Infinite Number ◽  
Dissipative Structure ◽  
Dissipative Structures ◽  
Area Theorem ◽  
Entropy Increase ◽  
The Universe

The area of the event horizon of a black hole (Aeh) is so far linked only with its entropy (SBH). In this theoretical investigation, it is shown that relating Aeh only to SBH is inadequate, because Aeh is linked to the black hole’s negentropy, which encompasses its entropy. Increasing Aeh of black holes that grow now follows from the negentropy theorem (NET) and also from the well-known area theorem. The decreasing Aeh of black holes that decay follows from the converse to NET and is not a violation of the area theorem. The corollary to NET is proved for the case when two dissipative structures merge, which is the basis for the coalescence of black holes. The converse of corollary to NET explains negentropy loss due to splitting of a dissipative structure. When applied to black hole explosion (i.e., splitting into an infinite number of parts), converse of corollary to NET reduces to converse of NET. The entropy/energy ratio of the exported Hawking radiance from black holes contributes to the entropy increase of the universe. These aspects justify the consideration of black holes as thermodynamic dissipative structures.

scholarly journals Twisted light, a new tool for general relativity and beyond — Revealing the properties of rotating black holes with the vorticity of light —

2021 ◽  
Author(s):  
F. Tamburini ◽  
F. Feleppa ◽  
B. Thidé
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Black Hole ◽  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Gravitational Lensing ◽  
Compact Object ◽  
Additional Tool ◽  
Physical Observable ◽  
Rotating Black Holes

We describe and present the first observational evidence that light propagating near a rotating black hole is twisted in phase and carries orbital angular momentum. The novel use of this physical observable as an additional tool for the previously known techniques of gravitational lensing allows us to directly measure, for the first time, the spin parameter of a black hole. With the additional information encoded in the orbital angular momentum, not only can we reveal the actual rotation of the compact object, but we can also use rotating black holes as probes to test general relativity.

BRANEWORLD BLACK HOLES IN COSMOLOGY AND ASTROPHYSICS

2005 ◽  
Vol 14 (07) ◽  
pp. 1095-1129 ◽  
Author(s):  
A. S. MAJUMDAR ◽  
N. MUKHERJEE
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Lensing ◽  
Strong Field ◽  
Planck Scale ◽  
High Energy ◽  
Field Equations ◽  
Large Extra Dimension ◽  
Gravitational Field Equations ◽  
Fundamental Scale

The braneworld description of our universe entails a large extra dimension and a fundamental scale of gravity that might be lower by several orders of magnitude compared to the Planck scale. An interesting consequence of the braneworld scenario is in the nature of spherically symmetric vacuum solutions to the brane gravitational field equations which could represent black holes with properties quite distinct compared to ordinary black holes in 4-dimensions. We discuss certain key features of some braneworld black hole geometries. Such black holes are likely to have diverse cosmological and astrophysical ramifications. The cosmological evolution of primordial braneworld black holes is described highlighting their longevity due to modified evaporation and effective accretion of radiation during the early braneworld high energy era. Observational abundance of various evaporation products of the black holes at different eras impose constraints on their initial mass fraction. Surviving primordial black holes could be candidates of dark matter present in galactic haloes. We discuss gravitational lensing by braneworld black holes. Observables related to the relativistic images of strong field gravitational lensing could in principle be used to distinguish between different braneworld black hole metrics in future observations.

scholarly journals Gravitational lensing effect on the Hawking radiation of dyonic black holes

2014 ◽  
Vol 11 (08) ◽  
pp. 1450074 ◽  
Author(s):  
Izzet Sakalli ◽  
Ali Ovgun ◽  
Seyedeh Fatemeh Mirekhtiary
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Refractive Index ◽  
Coordinate System ◽  
Gravitational Lensing ◽  
Hawking Radiation ◽  
Hawking Temperature ◽  
Tunneling Rate ◽  
Asymptotically Flat ◽  
Lensing Effect

In this paper, we analyze the Hawking radiation (HR) of a non-asymptotically flat (NAF) dyonic black hole (dBH) in four-dimensional (4D) Einstein–Maxwell–Dilaton (EMD) gravity by using one of the semiclassical approaches which is the so-called Hamilton–Jacobi (HJ) method. We particularly motivate on the isotropic coordinate system (ICS) of the dBH in order to highlight the ambiguity to be appeared in the derivation of the Hawking temperature (TH) via the HJ method. Besides, it will be shown that the ICS allows us to write the metric of the dBH in form of the Fermat metric, which renders possible of identification of the refractive index (n) of the dBH. It is unraveled that the value of n and therefore the gravitational lensing effect is decisive on the tunneling rate of the HR. We also uncloak how one can resolve the discrepancy about the TH of the dBH in spite of that lensing effect.

scholarly journals Shadows of Kerr black holes with and without scalar hair

2016 ◽  
Vol 25 (09) ◽  
pp. 1641021 ◽  
Author(s):  
Pedro V. P. Cunha ◽  
Carlos A. R. Herdeiro ◽  
Eugen Radu ◽  
Helgi F. Rúnarsson
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Analytical Solution ◽  
Ray Tracing ◽  
Gravitational Lensing ◽  
External Source ◽  
Numerical Examples ◽  
Arbitrary Position ◽  
Tracing Algorithm ◽  
Scalar Hair

For an observer, the Black Hole (BH) shadow is the BHs apparent image in the sky due to the gravitational lensing of nearby radiation, emitted by an external source. A recent class of solutions dubbed Kerr BHs with scalar hair possess smaller shadows than the corresponding Kerr BHs and, under some conditions, novel exotic shadow shapes can arise. Thus, these hairy BHs could potentially provide new shadow templates for future experiments such as the Event Horizon Telescope. In order to obtain the shadows, the backward ray-tracing algorithm is briefly introduced, followed by numerical examples of shadows of Kerr BHs with scalar hair contrasting with the Kerr analogues. Additionally, an analytical solution for the Kerr shadow is derived in closed form for a ZAMO observer at an arbitrary position.

scholarly journals Weak Deflection Angle of Kazakov-Solodukhin Black Hole in Plasma Medium

2021 ◽  
Author(s):  
Wajiha Javed ◽  
Iqra Hussain ◽  
Ali Övgün
Keyword(s):  
Black Hole ◽  
Gravitational Lensing ◽  
Deformation Parameter ◽  
Deflection Angle ◽  
Modern Method ◽  
Observational Evidence ◽  
Plasma Medium ◽  
Light Rays ◽  
The Deflection Angle ◽  
Bonnet Theorem

In this paper, we study light rays in a Kazakov-Solodukhin black hole. To this end, we use the optical geometry of the Kazakov-Solodukhin black hole within the Gauss-bonnet theorem. We first show the effect of the deformation parameter $a$ on the Gaussian optical curvature, and then we use the modern method popularized by Gibbons and Werner to calculate the weak deflection angle of light. Our calculations of deflection angle show how gravitational lensing is affected by the deformation parameter $a$. Moreover, we demonstrate the effect of a plasma medium on weak gravitational lensing by the Kazakov-Solodukhin black hole. We discuss that the increasing the deformation parameter $a$, will increase the weak deflection angle of the black hole. Our analysis also uncloak how one may find a observational evidence for a deformation parameter on the deflection angle.

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