Shadows and photon rings of regular black holes and geonic horizonless compact objects

Abstract

The optical appearance of a body compact enough to posses an unstable bound orbit, when surrounded by an accretion disk, is expected to be dominated by a luminous ring of radiation enclosing a central brightness depression known as the shadow, a picture fully backed up by the recent results of the EHT Collaboration. The characterization of both features -ring and shadowdepends on the interaction between the background geometry and the accretion disk, thus being a fertile playground to test our theories on the nature of compact objects and the gravitational field itself in the strong-field regime. In this work we use both features in order to test a continuous family of solutions interpolating between regular black holes and horizonless compact objects, which arise within the Eddington-inspired Born-Infeld theory of gravity, a viable extension of Einstein's General Relativity (GR). To this end we consider seven distinctive classes of such configurations (five black holes and two traversable wormholes) and study their optical appearances under illumination by a geometrically and optically thin accretion disk, emitting monochromatically with three analytic intensity profiles previously suggested in the literature. We build such images and consider the sub-ring structure created by light rays crossing the disk more than once and existing on top of the main ring of radiation. We discuss in detail the modifications as compared to their GR counterparts, the Lyapunov exponents of nearly unstable orbits, as well as the differences between black hole and traversable wormholes for the three intensity profiles. In addition we consider the properties of the shadow region and link them to the calibrated expectations by the EHT Collaboration. I. INTRODUCTIONA. Multimessenger quantum gravity era

Optical appearance of black holes surrounded by a dark matter halo

“…Many works in the field provide refinements to such a picture [19][20][21][22][23][24] or directly contest it via a supply of alternative black hole models (e.g. supported by additional matter fields or proposed within modifications of GR [25][26][27][28][29][30][31]) or instead using horizonless compact objects [32][33][34][35][36][37][38][39][40][41][42], providing a fertile playground to describe both black hole geometries and accretion disk physics via the images of ultra-compact objects [43][44][45][46]. Astrophysical black holes are not isolated objects.…”

Light Ring behind Wormhole Throat: Geodesics, Images and Shadows

“…Other types of compact objects, such as boson stars [12,13], naked singularities [14][15][16][17][18], quantum black holes [19][20][21][22][23] and wormholes [24][25][26][27][28][29][30][31], can also possess unstable photon orbits.…”