The images of supermassive black holes captured by the Event Horizon Telescope (EHT) collaboration have allowed us to have access to the physical processes that occur in the vicinity of the event horizons of these objects. Furthermore, black hole imaging gives rise to a new way of testing general relativity in the strong field regime. This has initiated a line of research aimed at probing different physical scenarios. While many scenarios have been proposed in the literature that yield distortion effects that would be a priori detectable at the resolution achieved by future EHT observations, the vast majority of those scenarios involve strange objects or exotic matter content. Here, we consider a less heterodox scenario which, involving non-exotic matter, in the sense that it satisfies all energy conditions and is dynamically stable, also leads to a deformation of the black hole shadow. We consider a specific concentration of non-emitting, relativistic matter of zero optical depth forming a bubble around the black hole. Due to gravitational refraction, such a self-interacting—dark—matter concentration may produce sub-annular images, i.e. subleading images inside the photon ring. We calculate the ray tracing in the space-time geometry produced by such a matter configuration and obtain the corresponding black hole images. While for concreteness we restrict our analysis to a specific matter distribution, modeling the bubble as a thin-shell, effects qualitatively similar to those described here are expected to occur for more general density profiles.

事件视界望远镜（EHT）合作捕获的超大质量黑洞图像使我们能够了解这些物体事件视界附近发生的物理过程。此外，黑洞成像提供了一种在强场范围内测试广义相对论的新方法。这引发了一系列旨在探索不同物理场景的研究。虽然文献中提出了许多产生畸变效应的场景，这些畸变效应在未来 EHT 观测所达到的分辨率下可以先验地检测到，但这些场景中的绝大多数都涉及奇怪的物体或奇异物质内容。在这里，我们考虑一个不那么非正统的场景，涉及非奇异物质，从某种意义上说，它满足所有能量条件并且是动态稳定的，也会导致黑洞阴影的变形。我们考虑特定浓度的零光学深度的非发射相对论物质在黑洞周围形成气泡。由于引力折射，这种自相互作用的暗物质浓度可能会产生亚环图像，即光子环内的亚主导图像。我们计算这种物质配置产生的时空几何中的射线追踪，并获得相应的黑洞图像。虽然为了具体起见，我们将分析限制在特定的物质分布上，将气泡建模为薄壳，但对于更一般的密度分布，预计会出现与此处描述的定性相似的效果。