General relativistic theory of charged accretion disk structures around black holes: influence of the (self)-electromagnetic interaction

• Applicant: Professor Dr. Claus Lämmerzahl
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields ; Astrophysics and Astronomy
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 510727404

In this project, we focus on accretion disks as charged perfect fluids. Electromagnetic fields are well known to have a strong influence on the structure, physics and evolution of accretion disks around compact objects like black holes or neutron stars. Since black holes cannot be observed directly and since accretion disks can approach the central compact object very closely, they are a perfect probe of the strong gravity or near-horizon regime and of the physics of the black holes and neutron stars. A full analysis of accretion disks has to include a combination of a variety of settings and influences. In case of an accretion disk made of a charged fluid, the influence of the charge of the disk on itself appears as one of the inevitable effects which are still mainly unexplored. For such complex problems, it is natural to first study the situation using idealized models offering analytic approaches, which provide a -- within the model -- thorough insight into the physical mechanisms. For a complete understanding general relativistic magneto-hydrodynamical simulations have to be carried through. Our primary focus is on accretion disks modeled by an ideal charged fluid within the geometrically thick disk framework. We will proceed in three steps: (i) We will determine the influence of the electromagnetic self-interaction on the disk. To start with, the electromagnetic field of the disk will be described as emerging from a charged ring on the disk center and acting on the disk. In a successive approximation procedure, we will determine the Faraday tensor of the entire disk. We will describe the influence of the induced field on the properties of the accretion disk. (ii) We study the oscillations and stability of the charged thick disk model including the self-field determined in (i). We analyse the oscillation modes and compare that result with the observations of high frequency quasi-periodic oscillations. From second order analysis of applied perturbations, we then will investigate the temporal evolution of the various charged thick equilibrium solutions. (iii) Finally, if time permits, we will consider a toy model to reproduce the polarized image of the center of M87 released by the Event Horizon Telescope collaboration. This image depends, among many other effects, on the magnetic field geometry and the space-time curvature. In all cases we try to find exact or approximate analytic solutions. In cases where this is impossible we will also apply numerical methods.

• DFG Programme: Research Grants
• Co-Investigator: Privatdozentin Dr. Eva Hackmann