Particle Acceleration Driven by Null Electromagnetic Fields Near a Kerr Black Hole

Yasufumi Kojima,Yuto Kimura

doi:10.3390/universe7010001

Abstract

Short timescale variability is often associated with a black hole system. The consequence of an electromagnetic outflow suddenly generated near a Kerr black hole is considered assuming that it is described by a solution of a force-free field with a null electric current. We compute charged particle acceleration induced by the burst field. We show that the particle is instantaneously accelerated to the relativistic regime by the field with a very large amplitude, which is characterized by a dimensionless number κ. Our numerical calculation demonstrates how the trajectory of the particle changes with κ. We also show that the maximum energy increases with κ2/3. The typical maximum energy attained by a proton for an event near a super massive black hole is Emax∼100 TeV, which is enough observed high-energy flares.

Highlights

For the first time, the event horizon telescope (EHT) team [1] acquired a near-horizon image of a nearby galaxy M87, which is an example of an supermassive black holes (SMBHs)
Our calculation of charged particle motion driven by null electromagnetic field is relevant to the direct acceleration mechanism
We examined the burst field under strong gravity near a black hole

Summary

Introduction

The magnetosphere is governed by the highly nonlinear equations of FFE, and the analytic solutions are limited; the simplest being a split-monopole solution [3] It describes a radial magnetic field near the center and a rotation-induced outward electromagnetic field at infinity. The solutions were characterized by the fact that two Lorentz invariant scalars vanish: ~E · ~B = 0 and B2 − E2 = 0 Such an electromagnetic field propagates at the speed of light, and the four-current is a null vector. Through the numerical calculations of time-dependent FFE, it is well known that current sheets may develop within the black hole magnetospheres [13,16,19,32]. We expect that the null FFE field or the field approximated by it must appear as a burst near a black hole and propagate outwardly.

Electromagnetic Fields

Axially Symmetric Magnetosphere

Particle Acceleration

Results

Discussion