Observational Signatures of Black Hole Accretion: Rotating vs. Spherical Flows with Tilted Magnetic Fields

TL;DR

This study uses simulations to compare observational signatures of black hole accretion with different magnetic field orientations and inflow geometries, finding that many observational features are surprisingly insensitive to initial conditions.

Contribution

It introduces a comparison of non-rotating inflow onto rotating black holes with tilted magnetic fields, highlighting the robustness of certain observational signatures across different initial conditions.

Findings

Polarization orientation is insensitive to initial magnetic field tilt.

Electron temperature models have a larger impact than accretion flow variations.

Spherical inflow produces kink-unstable jets.

Abstract

We study the observational signatures of magnetically arrested black hole accretion with non-rotating inflow onto a rotating black hole; we consider a range of angles between the black hole spin and the initial magnetic field orientation. We compare the results of our General Relativistic Magneto-Hydrodynamic simulations to more commonly used rotating initial conditions and to the Event Horizon Telescope (EHT) observations of M87. We find that the mm intensity images, polarization images, and synchrotron emission spectra are very similar among the different simulations when post-processed with the same electron temperature model; observational differences due to different electron temperature models are significantly larger than those due to the different realizations of magnetically arrested accretion. The orientation of the mm synchrotron polarization is particularly insensitive to the initial magnetic field orientation, the electron temperature model, and the rotation of the inflowing plasma. The largest difference among the simulations with different initial rotation and magnetic tilt is in the strength and stability of the jet; spherical inflow leads to kink-unstable jets. We discuss the implications of our results for current and future EHT observations and for theoretical models of event-horizon-scale black hole accretion.