arXiv subjects

Zeng-Yi Zhang

Publications and source records attributed to Zeng-Yi Zhang.

3 recordsLinked to original sources

arXiv2026

Near-extremal asymptotics and strong cosmic censorship for black holes immersed in a Chaplygin-like dark fluid

We investigate strong cosmic censorship (SCC) for massless scalar perturbations of electrically neutral black holes immersed in a Chaplygin-like dark fluid (CDF). The matter distribution produces an asymptotically de Sitter exterior while supporting an inner Cauchy horizon. We derive a closed-form parametrization of the extremal and Nariai horizon boundaries. This analytic control yields explicit near-extremal asymptotics for the horizon splitting and Cauchy-horizon surface gravity, together with an analytic expression for the leading near-extremal scalar quasinormal spectrum. The fundamental near-extremal damping rate approaches the Cauchy-horizon surface gravity, whereas higher angular multipoles retain explicit dependence on the CDF extremal geometry. Combining these analytic results with global quasinormal-mode calculations, we determine the spectral gap and assess the Christodoulou formulation of SCC throughout the three-horizon domain. Potential SCC violation is confined to a narrow region near extremality. As the effective cosmological scale increases, the lower boundary of this region is controlled successively by de Sitter, photon-sphere, and de Sitter modes, while its normalized width varies nonmonotonically.

gr-qc↗

arXiv2026

Optical Appearance of the Kerr-Bertotti-Robinson Black Hole with a Magnetically Driven Synchrotron Emissivity Model

We investigate the optical appearance of a Kerr-Bertotti-Robinson (Kerr-BR) black hole illuminated by a geometrically and optically thin accretion disk. Instead of using a phenomenological power-law emissivity, we adopt a magnetically driven synchrotron emissivity proxy coupled to the local electromagnetic environment. With a backward ray-tracing framework, we examine the effects of the spin $a$, magnetic parameter $B$, and observer inclination $θ_O$ on the ray-classification maps, redshift distributions, and specific-intensity images. We show that the ISCO position is modified by both $a$ and $B$, and that rapidly rotating prograde configurations can develop an additional model-dependent inner cutoff when the magnetically dominated approximation underlying the emissivity prescription ceases to be applicable. High-resolution one-dimensional intensity profiles further separate the direct image, the $n=1$ lensing-ring contribution, and the higher-order $n\geq 2$ photon-ring subimages, while quantifying the Doppler-induced brightness asymmetry. Retrograde disks exhibit a wider emission-depleted central region because of the outwardly shifted ISCO, making the higher-order lensed components more clearly distinguishable from the direct emission. These results show that the disk inner boundary and the magnetic-field-dependent emissivity can substantially influence the observable appearance of Kerr-BR black holes.

astro-ph.HE↗

arXiv2025

Black holes immersed in modified Chaplygin-like dark fluid and cloud of strings: shadows, quasinomal modes and greybody factors

We present a unified investigation of black hole shadows, quasinormal modes (QNMs), and greybody factors (GBFs) for a static, spherically symmetric black hole within a composite environment of a modified Chaplygin-like dark fluid (MCDF) and a cloud of strings (CoS). We examine the structure of critical photon orbits and the corresponding optical appearance under spherical accretion. Using the Wentzel-Kramers-Brillouin (WKB) approximation, we compute the quasinormal frequencies and greybody spectra, and explore their correspondence with the black hole shadows in the eikonal limit. A systematic parameter study demonstrates that the CoS intensity has the primary influence on the shadows, QNMs and GBFs, while the MCDF parameters introduce more complex but characterizable modifications to each. Our results demonstrate that these environmental components imprint distinct yet interrelated signatures on key observables, offering specific predictions for probing exotic black hole environments.

gr-qc↗