Magnifications Of Relativistic Images Research Articles

Strong Gravitational Lensing for the Quantum-Modified Schwarzschild Black Hole

We research the strong gravitational lensing for the quantum-modified Schwarzschild black hole which is derived from quantum Raychaudhuri equation. With the increase of quantum Raychaudhuri equation parameter η, we find that the distance between the black hole and the light passing by it becomes smaller; the deflection angle gets larger; the magnification of relativistic images is more similar; all of the relativistic images move towards the black hole while the images are farther to each other. These results, as we expect, will degenerate to the case of Schwarzschild black hole when $\eta \rightarrow 0$ .

Strong gravitational lensing by regular electrically charged black holes

In nonlinear electrodynamics a photon does not follow null geodesics of background geometry, but moves along null geodesics of a corresponding effective geometry. Therefore, in the strong deflection limit, in order to study the gravitational lensing of the regular electrically charged black holes obtained by coupling general relativity to nonlinear electrodynamics, one should firstly obtain the corresponding effective geometry, which is a necessary and key step. I obtain the deflection angle of the photon in the strong deflection limit, and further calculate the angular position and magnification of relativistic images. It is found that, the electric charge has significant effect on the gravitational lensing of regular black holes. With the increase of the electric charge q, the angular position of the relativistic images $$\theta _{\infty }$$ and the relative magnification $$\mathcal {R}_{m}$$ as a function of q decrease, while the angular separation between the outermost relativistic image and the others $$\mathcal {S}$$ as a function of q increases. I also discuss the measurement of observables for the black hole at the center of our Galaxy in the cases of regular electrically charged black hole effective metrics.

Regular Magnetic Black Hole Gravitational Lensing**Supported by the Natural Science Foundation of Education Department of Shannxi Province under Grant No 15JK1077, and the Doctorial Scientific Research Starting Fund of Shannxi University of Science and Technology under Grant No BJ12-02.

The Bronnikov regular magnetic black hole as a gravitational lens is studied. In nonlinear electrodynamics, photons do not follow null geodesics of background geometry, but move along null geodesics of a corresponding effective geometry. To study the Bronnikov regular magnetic black hole gravitational lensing in the strong deflection limit, the corresponding effective geometry should be obtained firstly. This is the most important and key step. We obtain the deflection angle in the strong deflection limit, and further calculate the angular positions and magnifications of relativistic images as well as the time delay between different relativistic images. The influence of the magnetic charge on the black hole gravitational lensing is also discussed.

Braneworld Black Hole Gravitational Lensing**Supported by Natural Science Foundation of Education Department of Shannxi Provincial Government under Grant No. 15JK1077, and Doctorial Scientific Research Starting Fund of Shannxi University of Science and Technology under Grant No. BJ12-02

A class of braneworld black holes, which I called as Bronnikov–Melnikov–Dehen (BMD) black holes, are studied as gravitational lenses. I obtain the deflection angle in the strong deflection limit, and further calculate the angular positions and magnifications of relativistic images as well as the time delay between different relativistic images. I also compare the results with those obtained for Schwarzschild and two braneworld black holes, i.e., the tidal Reissner-Nordström (R-N) and the Casadio–Fabbri–Mazzacurati (CFM) black holes.

Gravitational lensing in the presence of plasmas and strong gravitational fields

The theory of gravitational lensing is well developed for light propagation in vacuum in the approximation of weak deflection. We discuss two ways of extending the studies of usual gravitational lens theory which were recently theoretically developed. One way is to go beyond the weak deflection approximation and consider relativistic images formed by the photons performing one or several revolutions around the central object. Another way is to consider the propagation of light in a plasma instead of vacuum, in the presence of gravity. In this case the lensing angle depends on the plasma distribution and the photon frequency. The gravitational deflection of a light ray even in a homogeneous plasma differs from the vacuum (Einstein) angle and depends on the photon frequency. We also discuss the recent results on the influence of a plasma on positions and magnifications of relativistic images.

Gravitational lensing in plasma: Relativistic images at homogeneous plasma

We investigate the influence of plasma presence on relativistic images formed by Schwarzschild black hole lensing. When a gravitating body is surrounded by a plasma, the lensing angle depends on a frequency of the electromagnetic wave due to refraction properties, and the dispersion properties of the light propagation in gravitational field in plasma. The last effect leads to a difference, even in uniform plasma, of the gravitational deflection angle in plasma from the vacuum case. This angle depends on the photon frequency, which resembles the properties of the refractive prism spectrometer. Here we consider the case of a strong deflection angle for the light, traveling near the Schwarzschild black hole, surrounded by a uniform plasma. Asymptotic formulas are obtained for the case of a very large deflection angle, exceeding $2\ensuremath{\pi}$. We apply these formulas for calculation of position and magnification of relativistic images in a homogeneous plasma, which are formed by the photons performing one or several revolutions around the central object. We conclude that the presence of the uniform plasma increases the angular size of relativistic rings or the angular separation of point images from the gravitating center. The presence of the uniform plasma increases also a magnification of relativistic images. The angular separation and the magnification become significantly larger than in the vacuum case, when the photon frequency goes to a plasma frequency.