Motion Of Light Rays Research Articles

Can a light ray distinguish the charge of a black hole in nonlinear electrodynamics?

It is a well-known fact that light rays do not follow the null geodesics of the space-time in nonlinear electrodynamics; instead, they follow the null geodesics of the so-called effective space-time. Taking this into account, in this paper, we aim to discuss the possibility of distinguishing the type of charge with which the black hole is endowed, via the motion of light rays. The results show that, for any black hole being a charged solution of the field equations of general relativity coupled to the nonlinear electrodynamics, one cannot distinguish the two types of charge (magnetic or electric) through the motion of light rays around it.

Higher order corrections to deflection angle of massive particles and light rays in plasma media for stationary spacetimes using the Gauss-Bonnet theorem

The purpose of this article is twofold. First, we extend the results presented in [Gabriel Crisnejo and Emanuel Gallo, Phys.Rev.D 97, 124016 (2018)] to stationary spacetimes. Specifically, we show that the Gauss-Bonnet theorem can be applied to describe the deflection angle of light rays in plasma media in stationary spacetimes. Second, by using a correspondence between the motion of light rays in a cold non magnetized plasma and relativistic test massive particles we show that this technique is not only powerful to obtain the leading order behavior of the deflection angle of massive/massless particles in the weak field regime but also to obtain higher order corrections. We particularize it to a Kerr background where we compute the deflection angle for test massive particles and light rays propagating in a non homogeneous cold plasma by including third order corrections in the mass and spin parameters of the black hole.

Effect of non zero cosmological constant on the motion of light ray

Cosmological constant, the value of the energy density of the vacuum of space, was introduced by Einstein as an extension of general relativity. Recent studies show that cosmological constant has a noticeable effect on the shape of space-time i.e. it will influence the path of light ray. In this study the effect of non-zero cosmological constant on the path of light ray in three different types of space-time geometry namely Schwarzschild de Sitter, Kerr de Sitter and Kerr- Newman de Sitter has been discussed.

Massive motion in area metric spacetimes

The motion of massive point matter in area metric spacetimes, which arise as refinements of the Lorentzian spacetime structure in various situations of physical interest, is shown to be governed by a Finslerian geometry. This finding is based on the study of interacting string fluids on area metric manifolds, and extends previous findings on the motion of light rays.

R- and T-Regions in Space-Time with Spherically Symmetric Space

The properties of solutions of Einstein's equations for spherically symmetric gravitational fields are studied. The notions of R- and T-universe regions are introduced. T-regions are shown to be regions of essential instability in the distinguished direction of the flow of time. The geometrical properties and those of the deformation of reference frames in these regions are discussed. Birkhoff's theorem for the Schwarzschild field is stated more precisely. In a T-region of this field there exists a frame of reference with the interval in the form $$ds^2 = \left( {1 - \frac{{2{\text{ }}m}}{{c^3 t}}} \right)^{ - 1} c^2 dt^2 - \left( {1 - \frac{{2{\text{ }}m}}{{c^3 t}}} \right)dr^2 - c^2 t^2 (d{\text{ }}^{\text{2}} + \sin ^2 {\text{ }}d{\text{ }}^{\text{2}} ),$$ where t is the time coordinate, r the radial space coordinate, γ the Newtonian gravitational constant, c the fundamental velocity and m the mass producing the field. In this system, by comparison with Schwarzschild's, the space and time coordinates have changed places. The properties of the motion of light rays and test particles in R- and T-regions are discussed. The conclusions should be taken into account in considering cosmological questions and in the investigation of superdense stellar configurations.

Scattering map for two black holes

We study the motion of light in the gravitational field of two Schwarzschild black holes, making the approximation that they are far apart, so that the motion of light rays in the neighborhood of one black hole can be considered to be the result of the action of each black hole separately. Using this approximation, the dynamics is reduced to a two-dimensional map, which we study both numerically and analytically. The map is found to be chaotic, with a fractal basin boundary separating the possible outcomes of the orbits (escape or falling into one of the black holes). In the limit of large separation distances, the basin boundary becomes a self-similar Cantor set, and we find that the box-counting dimension decays slowly with the separation distance, following a logarithmic decay law.

Global effects due to a chiral cone

Scalar and spinor quantum particles are considered in the background space–time generated by a chiral cosmic string. It is shown that in this chiral conical space–time, the wave functions, the energy spectra, and the scattering amplitude associated with a quantum scalar particle depend on the global features of this space–time. In the case of a spinor particle, we study this dependence on the wave functions, energy, and current. These dependences represent gravitational analogues of the well-known Aharonov–Bohm effect in electrodynamics. Using the Hamilton–Jacobi equations, we also look into the motion of light rays and show how the effective potential depends on the global features of the chiral conical space–time.

Gravitational effects due to a cosmic string in Schwarzschild spacetime

Quantum particles are considered in the Schwarzschild spacetime containing a cosmic string. The effects due to the presence of the string on the physical states of particles are discussed. Using the Hamilton - Jacobi equation we look at the motion of light rays, determine the cross section for capture of particles and discuss the effect of the string in the range of variation of the classical states of energy.

Some gravitational effects in a locally flat Einstein-Maxwell spacetime

A spinor particle is considered in the background gravitational field due to a tubular matter source with axial interior magnetic field and vanishing exterior magnetic field. In the locally flat spacetime around this tubular matter source the authors study the gravitational analogue of Aharonov-Bohm effect for this particle. They also look at the motion of light rays and they discuss the existence of a self-force on an electric charge at rest in this background.

Fermat's principle in general relativity.

Kovner has observed that Fermat's principle can be used to describe the motion of light rays in arbitrary gravitational fields, not just stationary ones. We give a simple demonstration of this fact.

Motion of test particles and photons in the gravitational field of a cosmic string

The motion of light rays and test particles are studied in the gravitational field of a cosmic string. Using Hiscock's semiclassical cosmic string metric, it is found that some of the outgoing particles will traverse an infinite distance but some particles may be trapped by the string at a finite distance from the axis. For incoming particles also, some will reach the boundary of the string but some may face a potential barrier and cannot penetrate beyond a certain distance from the string.