arXiv subjects

Rogério Capobianco

Publications and source records attributed to Rogério Capobianco.

5 recordsLinked to original sources

arXiv2026

Photon rings and shadows of Kerr black holes immersed in a swirling universe

We discuss photon rings around as well as shadows of Kerr black holes immersed in a swirling spacetime (KBHSU). We find that the spin-spin interaction between the angular momentum of the black hole and the swirling of the background leads to new interesting effects as it breaks the symmetry between the upper and lower hemispheres. We find that a pair of light rings exists for all values of the parameter space. Using a topological argument, we prove that there should be, indeed, two light rings and that, additionally, these light rings are unstable. In comparison to the Schwarzschild black hole immersed in a swirling universe, the light rings typically all possess different radii. Interestingly, as the value of the swirling parameter is increased at fixed angular momentum of the black hole the two disconnected patches of the ergoregions eventually merge. The light ring at this merger possesses no angular velocity (as measured by an observer at infinity) and is called a \textit{light point}. To our knowledge, this is the first time the existence of such a light point in a black hole space-time is reported. Finally, we also present the shadows of KBHSU for various parameter values and observe that, due to the presence of the swirling background, the shadows are twisted.

gr-qc↗

arXiv2025

Accretion Structures around Kerr Black Holes in a Swirling Background

We investigate thick accretion structures around Kerr black holes in a swirling background. This stationary and axisymmetric spacetime is composed of a rotating black hole, which is immersed in a rotating background. The swirling background is characterized by an odd $\mathcal{Z}_2$ symmetry, where the northern and southern hemispheres are rotating in opposite directions. The presence of the Kerr rotation leads to the emergence of complex spin-spin interactions with the background rotation, which heavily influence the spacetime properties. In order to study this influence, we analyze circular orbits and geometrically thick disks for different spacetime solutions, that are classified by their Kerr parameter $a$ and the swirling parameter $j$. We identify stabilizing effects on prograde circular orbits and destabilizing effects on retrograde circular orbits, which originate from the spin-spin interaction and depend mainly on the Kerr rotation. Furthermore, we discovered the emergence of static orbits, which appear due to the background rotation. The symmetry breaking with regard to the equatorial plane causes a concave (convex) distribution of prograde (retrograde) circular orbits and accordingly, bowl-like deformations of the accretion disk structures. The parameter space for disk solutions gets heavily downsized by the appearance of an outer marginally stable orbit. Due to the possibility of an outer and inner disk cusp, different types of disk solutions are possible. We classify the different types of disk solutions, which differ from each other by the properties of their cusps. Four different scenarios can be identified in which different accretion dynamics could arise.

gr-qc↗

arXiv2024

Motion of charged particles in an electromagnetic swirling universe: The complete set of solutions

We discuss the motion of electrically and magnetically charged particles in the electromagnetic swirling universe. We show that the equations of motion can be decoupled in the Hamilton-Jacobi formalism, revealing the existence of a fourth constant of motion. The equations of motion can be analytically integrated. The solutions are presented in terms of elementary and elliptic functions. In addition, we discuss the possible orbits for both uncharged particles (in which case the motion is geodesic) and charged particles, respectively. A typical orbit is bounded in the radial direction and escapes to infinity in the $z-$ direction. However, the presence of the electromagnetic fields also leads to the existence of planar orbits.

gr-qc↗

arXiv2023

Geodesic Motion in a Swirling Universe: The complete set of solutions

We study the geodesic motion in a space-time describing a swirling universe. We show that the geodesic equations can be fully decoupled in the Hamilton-Jacobi formalism leading to an additional constant of motion. The analytical solutions to the geodesic equations can be given in terms of elementary and elliptic functions. We also consider a space-time describing a static black hole immersed in a swirling universe. In this case, full separation of variables is not possible and the geodesic equations have to be solved numerically.

gr-qc↗

arXiv2021

Spontaneous scalarization of self-gravitating magnetic fields

In this paper, we study the spontaneous scalarization of an extended, self-gravitating system which is static, cylindrically symmetric and possesses electromagnetic fields. We demonstrate that a real massive scalar field condenses on this Melvin magnetic universe solution when introducing a non-minimal coupling between the scalar field and (a) the magnetic field and (b) the curvature of the space-time, respectively. We find that in both cases, the solutions exist on a finite interval of the coupling constant and that solutions with a number of nodes $k$ in the scalar field exist. For case (a) we observe that the intervals of existence are mutually exclusive for different $k$.

gr-qc↗