The Role of Adaptive Ray Tracing in Analyzing Black Hole Structure

TL;DR

This paper introduces an adaptive ray tracing method for efficiently generating high-resolution black hole images, aiding the analysis of photon rings and their observational signatures.

Contribution

It presents a novel adaptive ray tracing approach that reduces computational effort while maintaining high image accuracy for black hole simulations.

Findings

Images with less than 0.1% mean squared error using 12x fewer rays

Adaptive ray tracing effectively captures photon ring substructures

Explores signatures of photon rings in interferometric data

Abstract

The recent advent of the Event Horizon Telescope (EHT) has made direct imaging of supermassive black holes a reality. Simulated images of black holes produced via general relativistic ray tracing and radiative transfer provide a key counterpart to these observational efforts. Black hole images have a wide range of physically interesting image structures, ranging from extremely fine scales in their lensed "photon rings" to the very large scales in their relativistic jets. The multi-scale nature of the black hole system is therefore suitable for a multi-scale approach to generating simulated images that capture all key elements of the system. Here, we present a prescription for adaptive ray tracing, which enables efficient computation of extremely high resolution images of black holes. Using the polarized ray-tracing code ipole, we image a combination of semi-analytic and GRMHD models, and we show that images can be reproduced with mean squared error of less than 0.1% even after tracing 12x fewer rays. We then use adaptive ray tracing to explore properties of the photon ring. We illustrate the behavior of individual subrings in GRMHD simulations, and we explore their signatures in interferometric visibilities.