Heating of accretion-disk coronae and jets by general relativistic magnetohydrodynamic turbulence

Turbulence in an accretion disk launches Alfvén waves (AWs) that propagate away from the disk along magnetic-field lines. Because the Alfvén speed varies with distance from the disk, the AWs undergo partial non-WKB reflection, and counter-propagating AWs subsequently interact, causing AW energy to cascade to small scales and dissipate. To investigate this process, we introduce an Elsasser-like formulation of general relativistic magnetohydrodynamics (GRMHD) and develop the theory of general relativistic reduced MHD in an inhomogeneous medium. We then derive a set of equations for the mean-square AW amplitude $M_{+}$and turbulent heating rate $Q$under the assumption that, in the plasma rest frame, AWs propagating away from the disk are much more energetic than AWs propagating toward the disk. For the case in which the background flow is axisymmetric and time independent, we solve these equations analytically to determine$M_{+}$and $Q$as functions of position. We find that, for an idealized thin disk threaded by a large-scale poloidal magnetic field, the AW energy flux is${\sim}(\unicode[STIX]{x1D70C}_{\text{b}}/\unicode[STIX]{x1D70C}_{\text{d}})^{1/2}\unicode[STIX]{x1D6FD}_{\text{net,d}}^{-1/2}$times the disk’s radiative flux, where$\unicode[STIX]{x1D70C}_{\text{b}}$and$\unicode[STIX]{x1D70C}_{\text{d}}$are the mass densities at the coronal base and disk midplane, respectively, and$\unicode[STIX]{x1D6FD}_{\text{net,d}}$is the ratio (evaluated at the disk midplane) of plasma-plus-radiation pressure to the pressure of the average vertical magnetic field. This energy flux could have a significant impact on disk coronae and outflows. To lay the groundwork for future global simulations of turbulent disk coronae and jets, we derive a set of averaged GRMHD equations that account for reflection-driven AW turbulence using a sub-grid model.

Hot plasma modes across Reissner–Nördstrom–de Sitter horizon in a Veselago medium

We investigate wave attributes of hot plasma around a Reissner–Nördstrom–de Sitter (RN-dS) metric in a Veselago medium. A perturbation scheme is implemented on general relativistic magnetohydrodynamical (GRMHD) equations that are further used for Fourier analysis. The linearly perturbed Fourier-analyzed GRMHD equations depict the dispersion of hot plasma waves. It is found that inclusion of charge in de Sitter space greatly affects the wave dispersion. A comparison of wave properties is presented, and results reassert the presence of the Veselago medium.

GENERAL RELATIVISTIC EQUILIBRIUM MODELS OF MAGNETIZED NEUTRON STARS

Magnetic fields play a crucial role in many astrophysical scenarios and, in particular, are of paramount importance in the emission mechanism and evolution of Neutron Stars (NSs). To understand the role of the magnetic field in compact objects it is important to obtain, as a first step, accurate equilibrium models for magnetized NSs. Using the conformally flat approximation we solve the Einstein's equations together with the GRMHD equations in the case of a static axisymmetric NS taking into account different types of magnetic configuration. This allows us to investigate the effect of the magnetic field on global properties of NSs such as their deformation.

Dispersion modes of hot plasma for a Schwarzschild – de Sitter horizon in a Veselago medium

Herein, we analyze the dispersion modes of hot plasma around the Schwarzschild – de Sitter event horizon in the presence of a Veselago medium (left-handed). For this purpose, we apply Arnowitt, Deser, and Misner 3+1 formalism to develop general relativistic magnetohydrodynamics (GRMHD) equations for the Schwarzschild – de Sitter space–time. Implementation of linear perturbation yields perturbed GRMHD equations that are used for the Fourier analysis of rotating (nonmagnetized and magnetized) plasma. Wave analysis is described by the graphical representation of the wave vector, refractive index, change in refractive index, and phase and group velocities. The outcome of this work supports the validity of a Veselago medium.

Magnetic collimation of relativistic jets: the role of the black hole spin

An ideal engine for producing ultrarelativistic jets is a rapidly rotating black hole threaded by a magnetic field. Following the 3+1 decomposion of spacetime of Thorne et al. (1986), we use a local inertial frame of reference attached to an observer comoving with the frame-dragging of the Kerr black hole (ZAMO) to write the GRMHD equations. Assuming θ-self similarity, analytical solutions for jets can be found for which the streamline shape is calculated exactly. Calculating the total energy variation between a non polar streamline and the polar axis, we have extended to the Kerr metric the simple criterion for the magnetic collimation of jets developed by Sauty et al. (1999). We show that the black hole rotation induces a more efficient magnetic collimation of the jet.