# Event horizon silhouette: implications to supermassive black holes M87* and SgrA*

## TL;DR

This paper shows that the black hole silhouette observed by the Event Horizon Telescope actually reveals the event horizon hemisphere, and discusses how accretion matter and disk position inform us about black hole spin.

## Contribution

It provides a new interpretation of the black hole silhouette as the event horizon hemisphere and links observational features to black hole spin estimation.

## Key findings

- Silhouette corresponds to the event horizon hemisphere.
- Position of the brightest point indicates high black hole spin.
- Method applied to M87* suggests spin around 0.75.

## 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, $a\simeq0.75$.