Influence of frame-dragging on magnetic null points near rotating black hole

TL;DR

This paper investigates how frame-dragging effects near rotating black holes influence magnetic null points and electric fields, which are crucial for understanding particle acceleration mechanisms in black hole environments.

Contribution

It provides a detailed visualization of magnetic and electric field structures near rotating black holes, highlighting the impact of black hole spin and motion on magnetic null points.

Findings

Magnetic null points depend on black hole spin and position relative to the horizon.

Electric fields at null points facilitate charged particle acceleration.

Null points can occur outside the ergosphere at high spin values.

Abstract

Understanding the mechanisms of particle acceleration from the vicinity of black holes poses a challenge. Electromagnetic effects are thought to be a prime suspect, but details still need an explanation. To this end, we study a three-dimensional structure of oblique magnetic fields near a rotating black hole in vacuum. It has been proposed that such a set-up can lead to efficient acceleration when plasma is injected near a magnetic null point. We focus our attention especially on the magnetic field in the immediate neighborhood of the magnetic null point, which was previously shown to occur in the equatorial plane. By employing the Line-Integral-Convolution (LIC) method, we visualize the magnetic field lines and explore the electric lines rising out of the equatorial plane. We show the magnetic field structure near the boundary of ergosphere, depending on the spin of the black hole. Electric field develops a non-vanishing component passing through the magnetic null point and ensuring efficient acceleration of charged particles from this particular location near horizon. We also examine the effect of translatory boost on the field lines. Similarly to the frame-dragging by rotation, the linear motion carries field lines along with the black hole. Position of the magnetic null point recedes from the black hole horizon as the spin parameter increases. For the extreme value of a=1 the null point can occur outside the ergosphere.