Toward a Full MHD Jet Model of Spinning Black Holes. I. Framework and a Split Monopole Example

Abstract

In this paper, we construct a framework for investigating the magnetohydrodynamical jet structure of spinning black holes (BHs), where electromagnetic fields and fluid motion are governed by the Grad–Shafranov equation and the Bernoulli equation, respectively. Assuming steady and axisymmetric jet structure, we can self-consistently obtain electromagnetic fields, fluid energy density, and velocity within the jet, given proper plasma loading and boundary conditions. Specifically, we structure the two coupled governing equations as two eigenvalue problems, and develop full numerical techniques for solving them. As an example, we explicitly solve the governing equations for the split monopole magnetic field configuration and simplified plasma loading on the stagnation surface where the poloidal fluid velocity vanishes. As expected, we find the rotation of magnetic field lines is dragged down by fluid inertia, and the fluid as a whole does not contribute to energy extraction from the central BH, i.e., the magnetic Penrose process is not working. However, if we decompose the charged fluid as two oppositely charged components, we find the magnetic Penrose process does work for one of the two components when the plasma loading is low enough.