Speaker
Description
Recent observations of polarized light from galactic cores motivate the study of polarized exotic compact objects (ECOs), which can mimic the features of black holes (BHs) in the strong-field regime of gravity. In this work, the properties of three ultra-compact classes of models containing light rings are studied — relativistic thin-shell fluid spheres, thin-shell gravitational vacuum stars, and self-gravitating scalar boson stars coupled minimally to gravity via a solitonic potential. This work simulates the orbit of a hot spot around the considered ECOs in the ray-tracing software GYOTO, producing polarizational signatures and observables such as integrated images of the Stokes parameters $I$, $Q$, $U$; their evolution during the orbit in the QU-plane, and the electric vector position angle (EVPA). Assuming a vertical magnetic field structure supported by observations by the GRAVITY and ALMA collaborations, the study focuses on qualitative differences between the models and in comparison with the BH scenario. One fluid star model mimicks the BH observables, while another gravastar produces notable differences in the EVPA curve. Regarding boson stars, the absence of a higher-order image causes one model to deviate from the expected signature of the $QU$-loop, eliminating it as a possible candidate. These results provide a useful tool to constrain the metric in current and future observations.