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GRMHD Launching of Resistive and Dynamo Active Disks

Vourellis, Christos

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Abstract

Astrophysical jets appear as linear collimated objects of high speed that are typically found in young stellar objects, X-Ray binaries, gamma-ray bursts, or active galactic nuclei. The physical procedures that lead to the development of these jets have been studied extensively in the past years. We believe that the launching of highly relativistic jets requires the existence of an accretion disk threaded by a strong magnetic field that rotates around a black hole. We perform general relativistic magnetohydrodynamic simulations of outflow launching from thin accretion disks. As in the nonrelativistic case, resistivity is essential for the mass loading of the disk wind. We implemented resistivity in the ideal GRMHD code HARM3D, which allows us to run simulations with larger physical grids, higher spatial resolution, and longer simulation time. We present the numerical details of the code and we show numerical test in the resistive regime that prove the robustness of the code. As a reference simulation, we consider an initially thin, resistive disk orbiting the black hole, threaded by a large-scale magnetic flux. As the system evolves, outflows are launched from the black hole magnetosphere and the disk surface. We mainly focus on disk outflows, investigating their MHD structure and energy output in comparison with the Poynting-dominated black hole jet. The disk wind encloses two components -- a fast component dominated by the toroidal magnetic field and a slower component dominated by the poloidal field. The disk wind transitions from sub- to super-Alfvenic speed, reaching velocities approximately 0.1c. We provide parameter studies varying spin parameter and resistivity level and measure the respective mass and energy fluxes. A higher spin strengthens the disk wind dominated by the toroidal component of the magnetic field along the inner jet. We disentangle a critical resistivity level that leads to a maximum matter and energy output for both, resulting from the interplay between reconnection and diffusion, which in combination govern the magnetic flux and the mass loading. For counterrotating black holes the outflow structure shows a magnetic field reversal. We also show the structure and direction of the electric field and its connection with the velocity and magnetic field vectors. Finally, we present the first fully dynamical simulation of dynamo generated poloidal magnetic field in a GRMHD environment. We simulate cases of both accretion tori and disks and we find induced magnetic field with both dipolar and quadrupolar structure. We follow the evolution of the field structure and strength and we show the launching of outflows from the torus/disk surface and the black hole magnetosphere.

Item Type: Dissertation
Supervisor: Fendt, apl. Prof. Dr. Christian
Place of Publication: Heidelberg
Date of thesis defense: 21 January 2020
Date Deposited: 27 Jan 2020 11:43
Date: 2020
Faculties / Institutes: The Faculty of Physics and Astronomy > Dekanat der Fakultät für Physik und Astronomie
Service facilities > Max-Planck-Institute allgemein > MPI for Astronomy
Subjects: 520 Astronomy and allied sciences
Controlled Keywords: Schwarzes Loch, Jet <Astronomie>, Akkretionsscheibe
Uncontrolled Keywords: black holes, accretion disks, astrophysical jets
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