Speaker
Description
The image of a black hole (BH) in an optically thin environment is expected to be characterized by a dark central region surrounded by a bright ring of a characteristic size. The BH shadow and the photon ring are believed to play an important role in producing these features, both of which are observed in horizon-scale images of supermassive BH candidates. In this talk, we show that a dynamically stable object with no event horizon or capture cross-section (i.e., no shadow), no light rings (i.e., non-ultracompact), and only moderate redshift is able to produce a similar appearance. As a proof of principle, we perform general relativistic magnetohydrodynamic simulations of accretion onto a stable boson star with a sextic potential. We find that a ring of stalled matter forms at a radius which, after gravitational lensing, matches the size of the bright ring expected from a black hole of the same mass. We discuss the robustness of this mechanism and the lifetime of such a structure, showing that it is possible for non-ultracompact exotic compact objects to mimic the expected appearance of black hole shadows in horizon-scale observations.