Shadow images of regular black hole with finite boundary

Abstract: Regular black hole is one of the bottom-up solutions designed to eliminate the singularity at the center of black holes. Its horizonless solution has gained interest recently to model ultracompact star. Despite interesting, this proposal is problematic due to the absence of a well-defined boundary. In this work, we introduce a novel regular black hole model inspired by the Hayward black hole, incorporating additional terms to define a clear and well-defined `surface' radius $R$. We analyze the null geodesics around the object, both horizonful and horizonless configurations, by studying the photon effective potential. We further simulate the shadow images of the object surrounded by a thin accretion disk. Our results indicate that for $R > 3M$ the horizonfull shadow differs slightly from that of a Schwarzschild black hole. In the horizonless configuration, we identify distinct inner light ring structures near the central region of the shadow image, which differ from those observed in horizonless Hayward black holes.