Reshaping the inner shadow of a Kerr black hole by a torn accretion disk

TL;DR

This study models torn accretion disks around Kerr black holes and uses relativistic ray-tracing to show how such disks dramatically reshape the black hole's inner shadow, revealing complex and novel shadow features.

Contribution

It introduces a phenomenological torn disk model and demonstrates how torn disk geometry significantly alters black hole shadow morphology, which is difficult to reproduce with standard models.

Findings

Torn disk geometry causes severe erosion of the inner shadow.

Novel shadow features include bifurcated shadows, crescent structures, and multiple rings.

Shadow morphology is governed by disk discontinuity and tilt angle.

Abstract

When an accretion flow extends to the event horizon, their intersection defines the contour of the inner shadow. However, the morphological evolution of this critical feature remains largely unexplored within a torn accretion disk system, a configuration comprising distinct sub-disks formed when a tilted disk is disrupted by frame-dragging. To address this, we phenomenologically construct a torn accretion disk model and numerically simulate the inner shadow of a Kerr black hole using relativistic backward ray-tracing. We discover that the torn disk geometry profoundly alters the black hole's observational signatures, inducing severe erosion of the inner shadow and generating novel features such as bifurcated shadows, crescent-like structures, and multiple orders of shadow rings. These exotic morphologies, which are predominantly governed by the spatial discontinuity between the sub-disks and the tilt angle of the outer sub-disk, are exceedingly difficult to replicate within standard equatorial accretion paradigms. Our findings demonstrate that these distinctive shadow structures hold significant potential to serve as robust diagnostic probes for torn accretion environments, simultaneously implying that relying solely on the inner shadow to test gravity theories is fundamentally insufficient.