Non-Topological Soliton Bardeen Boson Stars and Their Frozen States

Abstract

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 $\tilde{\omega}$, and the self-interaction parameter $\tilde{\eta}$. Our results reveal that the magnetic charge $\tilde{q}$ exhibits $\tilde{\eta}$-dependent critical values $\tilde{q}_c$, beyond which ($\tilde{q} > \tilde{q}_c$) Bardeen boson stars (BBSs) may transition into frozen states ($\tilde{\omega} \to 0$). 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-Nordstr\"{o}m (RN) black holes with equivalent mass and magnetic charge. Notably, the ADM mass of frozen BBSs is independent of $\tilde{\eta}$. Furthermore, light ring (LR) solutions exist universally across all tested combinations of $\tilde{q}$ and $\tilde{\eta}$, with all frozen BBSs exhibiting LRs whose outer radius $\tilde r_{\text{outer}}^{\text{LR}}$ is independent of $\tilde{\eta}$. Compared to magnetic RN black holes, frozen BBSs possess a smaller outer LR radius ($\tilde r_{\text{outer}}^{\text{LR}} < \tilde r_{\text{outer}}^{\text{LR, RN}}$).