The Effects of Tilt on the Time Variability of Millimeter and Infrared Emission from Sagittarius A*

TL;DR

This study uses simulations to show that a modest tilt between black hole spin and plasma angular momentum increases variability in millimeter and infrared emissions from Sagittarius A*, affecting flux, image size, and centroid motion.

Contribution

It demonstrates how a 24-degree tilt significantly enhances variability and alters observable features in black hole accretion flows, providing new insights into Sgr A*'s emission behavior.

Findings

150% increase in millimeter flux variability with tilt

Millimeter image centroid shifts by 3.7 microarcseconds over 28 hours

Tilted disks can be 10% larger in diameter at certain angles

Abstract

Using a combination of general-relativistic magnetohydrodynamics simulations and ray tracing of synchrotron emission, we study the effect of modest (24 degrees) misalignment between the black hole spin and plasma angular momentum, focusing on the variability of total flux, image centroids, and image sizes. We consider both millimeter and infrared (IR) observables motivated by Sagittarius A* (Sgr A*), though our results apply more generally to optically thin flows. For most quantities, tilted accretion is more variable, primarily due to a significantly hotter and denser "coronal" region well off the disk midplane. We find (1) a 150% increase in millimeter light curve variability when adding tilt to the flow; (2) the tilted image centroid in the millimeter shifts on a scale of 3.7 microarcseconds over 28 hours (5000 gravitational times) for some electron temperature models; (3) tilted disk image diameters in the millimeter can be 10% larger (52 versus 47 microarcseconds) than those of aligned disks at certain viewing angles; (4) the tilted models produce significant IR flux, similar to that seen in Sgr A*, with comparable or even greater variability than observed; (5) for some electron models, the tilted IR centroid moves by more than 50 microarcseconds over several hours, in a similar fashion to the centroid motion detected by the GRAVITY interferometer.