Yi-Ning Gu | Searcharxiv

arXiv2025

Light Rings, Accretion Disks and Shadows of Hayward Boson Stars

In this paper, we investigate the Einstein-Hayward gravity coupled to a complex scalar field without self-interaction. Using numerical methods, we construct a class of Hayward boson star solutions and examine their fundamental properties as well as the optical appearance of the accretion disk. Our results show that in the frozen state, both the quasi-horizon radius and the light ring radii increase with the magnetic monopole charge. Furthermore, using ray-tracing method, we find that for non-frozen states, the absence of an quasi-horizon results in the appearance of multiple photon rings within the shadow region of the accretion disks. In contrast, for frozen states, the presence of a quasi-horizon causes their images to resemble those of Schwarzschild black holes, with no additional photon rings appearing.

gr-qc↗

arXiv2025

Non-Topological Soliton Bardeen Boson Stars and Their Frozen States

We investigate a Bardeen model coupling Einstein gravity with nonlinear electromagnetic fields and non-topological soliton complex scalar fields, governed by the magnetic charge $\tilde{q}$, the complex scalar field frequency $\tildeω$, and the self-interaction parameter $\tildeη$. Our results reveal that the magnetic charge $\tilde{q}$ exhibits $\tildeη$-dependent critical values $\tilde{q}_c$, beyond which ($\tilde{q} > \tilde{q}_c$) Bardeen boson stars (BBSs) may transition into frozen states ($\tildeω \to 0$). These frozen states are characterized by a critical horizon whose radius $\tilde r^\mathrm{H}_{c}$ satisfies $\tilde r_{\text{inner}}^{\text{H,RN}} < \tilde r_{c} < \tilde r_{\text{outer}}^{\text{H,RN}}$, where $\tilde r_{\text{inner}}^{\text{H,RN}}$ and $\tilde r_{\text{outer}}^{\text{RN}}$ denote the inner and outer horizons of magnetic Reissner-Nordström (RN) black holes with equivalent mass and magnetic charge. Notably, the ADM mass of frozen BBSs is independent of $\tildeη$. Furthermore, light ring (LR) solutions exist universally across all tested combinations of $\tilde{q}$ and $\tildeη$, with all frozen BBSs exhibiting LRs whose outer radius $\tilde r_{\text{outer}}^{\text{LR}}$ is independent of $\tildeη$. Compared to magnetic RN black holes, frozen BBSs possess a smaller outer LR radius ($\tilde r_{\text{outer}}^{\text{LR}} < \tilde r_{\text{outer}}^{\text{LR, RN}}$).

gr-qc↗