Event horizon silhouette: implications to supermassive black holes M87* and SgrA* (1903.09594v2)

Abstract: We demonstrate that a dark silhouette of the black hole illuminated by a thin accretion disk and seen by a distant observer is, in fact, a silhouette of the event horizon hemisphere. The boundary of this silhouette is a contour of the event horizon equatorial circle if a thin accretion disk is placed in the black hole equatorial plane. A luminous matter plunging into black hole from different directions provides the observational opportunity for recovering a total silhouette of the invisible event horizon globe. The event horizon silhouette is projected on the celestial sphere within a position of the black hole shadow. A relative position of brightest point in the accretion disk with respect to the position of event horizon silhouette in the image of black hole in the galaxy M87, observed by the Event Horizon Telescope, corresponds to a rather high value of the black hole spin, $a\simeq0.75$.