Seminar of Theoretical Physics - Barbora Bezděková (26.10.2021)
Tuesday 26.10.2021, at 14:00 hod., Lecture room F2/125
Barbora Bezděková (Institute of Theoretical Physics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic):
On the Light Rays Propagating in Plasma Medium around Relativistic Objects
Abstract:
Bending of light in a strong gravitational field is one of the crucial predictions of general relativity. Studies focusing on the light trajectories in the relativistic systems usually suppose that the gravitating object causing the curvature of the trajectories is set in vacuum. However, it turns out that in many astrophysical systems this assumption is not valid and it is also necessary to include the effects of refractive and dispersive media (plasma) surrounding the object. Including the medium into considerations is important - it can cause the rays to change substantially their form. The impact of refractive and dispersive media around compact objects is typically considered in problems related to the gravitational lensing. In our work we focus on how the regions allowed for propagation of rays in and close to the equatorial plane of a rotating black hole are modified due to the presence of the refractive and dispersive media with various density profiles. We investigate media with the density distributions corresponding to typical profiles of lensing galaxies, as well as with a toy model of density distribution often used in the literature - nonsingular isothermal sphere. We show that the regions permitted for the rays in a medium are substantially reduced as compared with the corresponding regions in vacuum. We also study allowed regions as seen by observers freely falling onto the black hole.