Radiative Models of Sagittarius A* and M87 from Relativistic MHD Simulations

TL;DR

This paper discusses relativistic MHD simulations of Sagittarius A* and M87 to interpret millimeter VLBI observations, aiming to understand their accretion flows, emission geometries, and the potential detection of black hole shadows.

Contribution

It presents a comparison of radiative transfer calculations from GRMHD simulations with VLBI data, providing insights into the accretion flow geometries and emission regions of Sgr A* and M87.

Findings

Black hole shadow detection possible with future observations.

Constraints on Sgr A*'s accretion flow geometry.

Predictions for M87's jet launching region size.

Abstract

Ongoing millimeter VLBI observations with the Event Horizon Telescope allow unprecedented study of the innermost portion of black hole accretion flows. Interpreting the observations requires relativistic, time-dependent physical modeling. We discuss the comparison of radiative transfer calculations from general relativistic MHD simulations of Sagittarius A* and M87 with current and future mm-VLBI observations. This comparison allows estimates of the viewing geometry and physical conditions of the Sgr A* accretion flow. The viewing geometry for M87 is already constrained from observations of its large-scale jet, but, unlike Sgr A*, there is no consensus for its millimeter emission geometry or electron population. Despite this uncertainty, as long as the emission region is compact, robust predictions for the size of its jet launching region can be made. For both sources, the black hole shadow may be detected with future observations including ALMA and/or the LMT, which would constitute the first direct evidence for a black hole event horizon.