Silhouette of a Dressed Black Hole

Abstract In the case of the traditional standard disk with an inner radius of $3 \,r_{\mathrm{g}}$ (three Schwarzschild radii) around the Schwarzschild black hole, there appears to be a dark central shadow with a radius of about $3 \,r_{\mathrm{g}}$. In the case of a disk extending down to $1 \,r_{\mathrm{g}}$, on the other hand, we found that the radius of the dark shadow is about $2 \,r_{\mathrm{g}}$. These shadow sizes are different from that obtained by Falcke et al. (2000, AAA 073.155.002), where the shadow radius is about $2.6 \,r_{\mathrm{g}}$. This is because they considered an optically-thin spherical envelope, while we assumed an optically-thick luminous disk. In addition, we found that in an edge-on view the central shadow becomes a semicircle due to the projection effect. Such a silhouette of a dressed black hole throws light on the space-time structure of the hole as well as the type of surrounding disk.