Frequency-dependent effects of gravitational lensing within plasma

Abstract

The interaction between refraction from a distribution of inhomogeneous plasma and gravitational lensing introduces novel effects to the paths of light rays passing by a massive object. The plasma contributes additional terms to the equations of motion, and the resulting ray trajectories are frequency-dependent. Lensing phenomena and circular orbits are investigated for plasma density distributions N ∝ 1/r h with h ≥ 0 in the Schwarzschild space-time. For rays passing by the mass near the plasma frequency refractive effects can dominate, effectively turning the gravitational lens into a mirror. We obtain the turning points, circular orbit radii, and angular momentum for general h. Previous results have shown that light rays behave like massive particles with an effective mass given by the plasma frequency for a constant density h = 0. We study the behaviour for general h and show that when h = 2 the plasma term acts like an additional contribution to the angular momentum of the passing ray. When h = 3 the potential and radii of circular orbits are analogous to those found in studies of massless scalar fields on the Schwarzschild background. As a physically motivated example we study the pulse profiles of a compact object with antipodal hotspots sheathed in a dense plasma, which shows dramatic frequency-dependent shifts from the behaviour in vacuum. Finally, we consider the potential observability and applications of such frequency-dependent plasma effects in general relativity for several types of neutron star.

Shadow of rotating wormhole in plasma environment

“…The shadow of the sphericallysymmetric Ellis wormholes surrounded by plasma has been studied by Perlick et al (2015). The gravitational lensing and images of black hole in plasma environment has been recently studied in Bisnovatyi-Kogan and Tsupko (2010), Tsupko and Bisnovatyi-Kogan (2012), Morozova et al (2013), Perlick et al (2015), Er and Mao (2014), Atamurotov et al (2015), Rogers (2015). The transfer of radiation in an isotropic refractive, and dispersive medium using the Hamiltonian approach in a curved spacetime is studied in Bicak and Hadrava (1975) by applying the generalrelativistic kinetic theory.…”

Optical properties of black holes in the presence of a plasma: The shadow

“…As an example here we get the value for power h as 1 [22]. For this value we plot the radial dependence of the effective potential V eff of the radial motion of the photons defined as dr dσ…”

“…We would like to underline that very recently, influence of a non-magnetized cold plasma with the radially dependent density to black hole shadow has been studied in [7] using the different alternate approach. In addition Rogers [22] has studied the photon motion around black hole surrounded by plasma.…”

Recent developments in gravitational lensing: Theory and numerical modeling

“…Ref. 56. Moreover, in some extream case, e.g., bullet cluster, the temperature of the interstellar and intergalactic medium can be very high, as well as in the vicinity of black hole.…”

“…56 The plasma distribution significantly affects the appearance of the compact object for a distant observer by changing the poriton of the surface that is visible as a function of frequency. This introduces a frequency-dependence to the morphology of the light curves and can significantly alter their features compared to the vacuum case.…”