See my Youtube channel for some movies of my simulations!

In the local universe, including the center of our own galaxy (Sgr A* ), most supermassive black holes are surrounded by hot, thick, and dim accretion disks. Many of these black holes, like the one in the M87, launch relativistic jets powered by the rotational energy of the black hole itself. To understand how plasma behaves in spacetime – how it emits radiation, launches jets, and feeds the black hole – one of our best tools is supercomputer simulations using the equations of General Relativistic Magnetohydrodynamics (GRMHD).

Unfortunately, in the hot, weakly coupled plasmas around M87 and Sgr A* , protons and electrons are not in thermal equilibrium with each other. Since most simulations assume thermodynamic equilibrium it is impossible to directly predict the radiation emitted from most simulations without making additional assumptions in post-processing. This makes predictions for the images observed by the Event Horizon Telescope difficult.

Several simulated images of Sgr A*.
Images of Sgr A* from my simulations (Chael+ 2018a) with four different values of black hole spin and electron heating functions, as viewed by the EHT at 230 GHz.

In my research, I use the massively parallel code KORAL which moves beyond standard single-fluid GRMHD to a three-fluid approximation where electrons, ions, and photons exchange energy self-consistently. This method allows us to directly predict what the Event Horizon Telescope will see and how different models emit across the entire electromagnetic spectrum. In Chael+ 2018a I tested two physical mechanisms for electron heating in plasmas – turbulence and magnetic reconnection – to investigate how plasma microphysics changes the images and variability of Sgr A* at different frequencies. In Chael+ 2018b (in prep.), I applied the same method to M87’s jet and determined that the observed characteristics are well explained by a Magnetically Arrested Disc model, where extreme magnetic fields on the black hole choke accretion.

Zooming in on the M87 jet
Images of of the M87 jet at different frequencies from one of my MAD simulations (Chael+ 2018b). As the frequency increases, the brightest emission moves down the jet closer and closer to the black hole.
Images from my MAD simulations of M87 using damped turbulence (left) and magnetic reconnection (right)
230 GHz images from my MAD simulations of M87 using damped turbulence (left) and magnetic reconnection (right) to heat electrons

In Chael+ 2017, I made a major update to KORAL by adding code to evolve a population of nonthermal electrons in space, time, and energy in parallel with the thermal fluid. This represents the first time that spectral resolution of electron distributions is possible in grid-based accretion simulations. This method will open up new ground in understanding the nonthermal jet emission in M87 and nonthermal infrared and X-ray flares in Sgr A*.