Relativity Seminar
of the Institute of Theoretical Physics


Seminar is held on Tuesdays at 13:10 pm in the lecture room of the Institute
on the 10th floor of the department building at Trója, V Holešovičkách 2, Prague 8


April 8, 2025
Orbital Motion in Spacetimes Influenced by the Presence of Scalar and Electromagnetic Fields
Dr. Jiří Horák
Astronomical Institute of the Czech Academy of Sciences

The study investigates orbital motion of test particles near compact objects described by solutions involving massless scalar fields, electromagnetic fields, and nonlinear electrodynamics. Specifically, we analyze orbital dynamics in the Janis-Newman-Winicour, Janis-Newman-Winicour-Maxwell, Schwarzschild-Melvine, and Bonnor-Melvin spacetimes, comparing the results with those obtained for the Schwarzschild and Reissner-Nordström solutions. We examine the stability of circular orbits and the behavior of epicyclic frequencies under varying physical parameters. Our analysis shows that in certain cases the central object transitions into a naked singularity. Deviations from classical Schwarzschild and Reissner-Nordström solutions reveal conditions for the existence of multiple photon orbits or marginally stable orbits. In some instances, the geometry allows the presence of two photon orbits—one stable and one unstable—with an interesting connection to the region of stable orbits. We find that at lower intensities, the effects of the scalar field and electromagnetic fields are comparable and seemingly interchangeable. However, for a sufficiently strong scalar field, its influence becomes dominant, leading to the emergence of a distinct region of stable orbits near the naked singularity. These effects are illustrated within the framework of optical geometry using embedding diagrams. Based on arXiv:2501.13538.

April 29, 2025
TBA
Dr. Ana Alonso Serrano
Albert Einstein Institute
May 6, 2025
TBA
Dr. Marina David
KU Leuven
May 13, 2025
TBA
Prof. Valeri P. Frolov
University of Alberta

David Kubizňák                                                                                                  Oldřich Semerák