arXiv subjects

Chengjia Chen

Publications and source records attributed to Chengjia Chen.

5 recordsLinked to original sources

arXiv2026

Images of Braneworld black holes with radiatively inefficient accretion flows

Horizon-scale imaging acts as a transformative tool for probing spacetime geometry, enabling stringent tests of gravitational theories in the strong-field regime. The Casadio-Fabbri-Mazzacurati(CFM) black hole in braneworld contains an extra parameter that characterizes the tidal effects from the bulk geometry, making it highly valuable for this task. We perform general relativistic radiative transfer (GRRT) simulations and generate synthetic images consistent with Event Horizon Telescope observations of M87*. We find that the tidal parameter imprints nonmonotonic changes on the image morphology, underscoring the intricate coupling between spacetime geometry and the observable radiation from the accreting plasma. We also analyze the image-comparison metric using normalized cross-correlation coefficients and the DSSIM index and find that the magnitudes of these mismatches are on the order of 10^3, which implies that identifying braneworld black holes through black hole images remains challenging even with future ngEHT and BHEX observations.

gr-qc↗

arXiv2025

Near-horizon polarized images of a rotating hairy Horndeski black hole

Recently, Hou \emph{et al.} [Astrophys. J. Lett. \textbf{988}, L51 (2025)] revealed that the Electric Vector Position Angle (EVPA) of polarization vectors in the near-horizon images is governed solely by the spacetime geometry and is irrespective of the plasma flows. Here, we generalize the study to the scenario of a rotating hair black hole within the Horndeski gravity and probe the effects of the hairy parameter on the EVPA. For a fixed inclination, the hairy parameter enhances the observed EVPA in the slowly rotating case, but decreases it in the rapidly rotating case. For a fixed black hole spin, the influence of the hairy parameter on the observed EVPA under different observer inclinations is further modulated by the azimuthal angle of the observed polarization vector. The hairy parameter's impact is more distinct in the low inclination case as the azimuthal angle lies within a specific range, but is almost independent of the observer inclination as the azimuthal angle is beyond this specific range. Furthermore, the dependence of the hairy parameter's impact on the EVPA is stronger with respect to the black hole spin than to the inclination angle. These results could help to further understand the near-horizon polarized images and Horndeski gravity.

gr-qc↗

arXiv2024

Precessions of spherical orbits in the rotating Melvin black hole spacetime and its constraints from the jet of M87*

We investigate precessions of spherical orbits of timelike particles in the background of a rotating black hole immersed in the Melvin magnetic field, and probe effects of the magnetic field on the precession period. Our results show that effects of the magnetic field on the particles' motions gradually decrease with the titled angle and finally vanish as the titled angle tends to $\pi/2$. With the increase of the magnetic field parameter, we find that the precession becomes rapidly. Modelling the spherical orbit to the warp radius in the accretion disk and with the observed precession period from the jet of M87*, we analyze the allowed regions of the black hole parameters and the warp radius in the accretion disk. Especially, we find a novel degenerated phenomenon of precession periods arising from magnetic field for two different spherical orbits, which does not appear in the usual Kerr black hole case. Moreover, we also discuss the possibility of observing effects of the magnetic field on the precession periods of jets for astrophysical black holes. Our study could help to further understand the rotating Melvin black hole and the relationship between magnetic fields and precessions of jets.

gr-qc↗

arXiv2024

Geometrically thick equilibrium tori around a Schwarzschild black hole in swirling universes

We study geometrically thick non-self gravitating equilibrium tori orbiting a Schwarzschild black hole immersed in swirling universes. This solution is axially symmetric and non-asymptotically flat, and its north and south hemispheres spin in opposite directions. Due to repulsive effects arising from the swirl of the background spacetime, the equilibrium torus exists only in the case with the small swirling parameter. With the increase of the swirling parameter, the disk structure becomes small and the excretion of matter near the black hole becomes strong. Moreover, the odd $Z_2$ symmetry of spacetimes originating from the swirling parameter yields that the orientation of closed equipotential surfaces deviates away from the horizontal axis and the corresponding disk does not longer possess the symmetry with respect to the equatorial plane. These significant features could help to further understand the equilibrium tori and geometrically thick accretion disks around black holes in swirling universes.

gr-qc↗

arXiv2023

Quasinormal modes of a scalar perturbation around a rotating BTZ-like black hole in Einstein-bumblebee gravity

We analytically study the quasinormal modes of a scalar perturbation around a rotating BTZ-like black hole in the Einstein-bumblebee gravity. We observe that the Lorentz symmetry breaking parameter imprints only in the imaginary parts of the quasinormal frequencies for the right-moving and left-moving modes. The perturbational field decays more rapidly for the negative Lorentz symmetry breaking parameter, but more slowly for the positive one. The forms of the real parts are the same as those in the usual BTZ black holes. Moreover, we also discuss the $AdS/CFT$ correspondence from the quasinormal modes and find that the Lorentz symmetry breaking parameter enhances the left and right conformal weights $h_L$ and $h_R$ of the operators dual to the scalar field in the boundary. These results could be helpful to understand the $AdS/CFT$ correspondence and the Einstein-bumblebee gravity with the Lorentz symmetry violation.

gr-qc↗