Preview

PDF, English Download (21MB) | Terms of use

Abstract

Astrophysical jets, consisting of collimated high-speed outflows, are typically found in several astrophysical objects, e.g., young stellar objects, X-ray binaries, gamma-ray bursts, or active galactic nuclei. The formation of collimated outflows requires some common features, such as the presence of a central object, an accretion disk and a large scale magnetic field (whose origin is still unclear). Regarding the numerical aspects, we compared several solutions of the Riemann problem for ideal relativistic plasma in terms of accuracy and robustness against one – and multidimensional standard numerical benchmarks. We then performed non-ideal Magnetohydrodynamic simulations by employing the PLUTO code in order to investigate how the mean-field dynamo and the magnetic diffusivity affect the disk and jet properties. At first we have investigated a non-isotropic dynamo toy model in order to disentangle the effect of the different dynamo components on the launching process and on the disk magnetic field. Then, we investigated a disk dynamo that follows analytical solutions of the mean-field dynamo theory, essentially based mainly on the Coriolis number. We thereby confirmed the anisotropy of the dynamo tensor acting in accretion disks, allowing both the resistivity and the mean-field dynamo to be related to the disk turbulence. Subsequently, we studied the feedback of the generated magnetic field on the mean-field dynamo. We found that a stronger quenching of the dynamo leads to a saturation of the magnetic field at a lower disk magnetization. Nevertheless, we found that, when applying only a dynamo quenching, the overall jet properties do not depend on the feedback model. Finally, we present a feedback model which encompasses a quenching of the magnetic diffusivity. We find that after the magnetic field is saturated the Blandford-Payne mechanism takes place yielding to more collimated yet slower jets. We find strong intermittent periods of flaring and knot ejection for low Coriolis numbers.