FNWI --- IMAPP Department of Astrophysics
Radboud University > Faculty of Science > Department of Astrophysics

MHD Simulations

Density profile of an accretion disk and jetThis image shows a vertical cut through the accretion disk, half of which is visible. Colours indicate the density of the gas, with black being the lowest and red being the highest. It can be seen that the jet has a very low density, sweeping out conical volumes following the vertical axis. The accretion disk possibly plays a role in collimating the jet.

Although several models for the structure and behaviour of relativistic jets (such as the jets that form at AGN) exist, these models mainly describe the evolution of the jet over larger distances once it has formed. Commonly, the base of a relativistic jet is considered to be the region where the outflowing gas goes supersonic.

What happens in order to make the gas form a jet in the first place depends on the circumstances it experiences closer to the black hole, such as the density of the environmental gas and the type of accretion disk (thin, slim, or thick) that surrounds the black hole. To better understand the role that these circumstances play in the resulting characteristics of the jet, we perform MHD simulations of the region closest to the black hole. In this region, we study how the initially Poynting-dominated jet is formed (i.e. consisting mainly of electromagnetic radiation, generated by the Blandford-Znajek effect) and how this initial jet sweeps up particles to turn into a mass-loaded jet.

Studies of the regions where particles get entrained in the jet and the way they are accelerated to high energies allow us to make more accurate predictions of the appearance of the jet in different wavelength bands. Testing these predictions against observational data then makes it possible to validate the models we make for jet generation.