Visible Shapes of Black Holes M87* and SgrA*

Vyacheslav I Dokuchaev,Natalia O Nazarova

doi:10.3390/universe6090154

Abstract

We review the physical origins for possible visible images of the supermassive black hole M87* in the galaxy M87 and SgrA* in the Milky Way Galaxy. The classical dark black hole shadow of the maximal size is visible in the case of luminous background behind the black hole at the distance exceeding the so-called photon spheres. The notably smaller dark shadow (dark silhouette) of the black hole event horizon is visible if the black hole is highlighted by the inner parts of the luminous accreting matter inside the photon spheres. The first image of the supermassive black hole M87*, obtained by the Event Horizon Telescope collaboration, shows the lensed dark image of the southern hemisphere of the black hole event horizon globe, highlighted by accreting matter, while the classical black hole shadow is invisible at all. A size of the dark spot on the Event Horizon Telescope (EHT) image agrees with a corresponding size of the dark event horizon silhouette in a thin accretion disk model in the case of either the high or moderate value of the black hole spin, a≳0.75.

Highlights

The enigmatic black holes are really black objects in the sky due to their physical properties.The famous quantum Hawking thermal radiation of black holes can be neglected in the case of numerous astrophysical black holes originated from the gravitational collapse of old massive stars.Nowadays, the only way to view black holes in the sky is a watching of black hole candidates highlighted by the surrounding matter
Image agrees with a corresponding size of the dark event horizon silhouette in a thin accretion disk model in the case of either the high or moderate value of the black hole spin, a & 0.75
We show that the unique physical properties of the Kerr metric for rotating black hole [7] provide two qualitatively different forms of the visible black images: the standard black hole shadow or the notably smaller event horizon shadow

Summary

Introduction

The enigmatic black holes are really black objects in the sky due to their physical properties. A notably smaller event horizon silhouette is viewed, which is a shadow of the event horizon itself, in the case of emitting matter placed inside the photon spheres (e.g., if there is a highly luminous accreting matter in the vicinity of the event horizon) To distinguish these two different black hole images, we will use in the following the term “classical black hole shadow”. The brightness of the accreting disk greatly exceeds the corresponding one of the distant luminous background, consisting of the extended hot gas clouds and bright stars For this reason, the classical black hole shadow is complicated to observe in comparison with the event horizon silhouette (the shadow of the event horizon itself). The contour integrals in (11) in the case of the trajectory with two turning points θmin (λ, q) and rmin (λ, q) (the extreme point in the radial effective potential R(r)), are written through the ordinary integrals in the form rs rmin dr r0 rmin θs θmin dθ p (17)

Classical Black Hole Shadow

Photon Spheres

Event Horizon Silhouette

Discussions

Results