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Motion of a charged test particle around a static black hole in a monopole magnetic field

Ken-ichi Nakao1,2,3,*, Yota Endo1, Hideki Ishihara2,3, Kenta Matsuo1, Kensuke Sueto1, Koudai Ueda3, and Hirotaka Yoshino1,2,3

  • *Contact author: knakao@omu.ac.jp
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Phys. Rev. D 114, 044019 – Published 6 August, 2026

DOI: https://doi.org/10.1103/9ppp-8xcv

Abstract

We study the motion of a charged test particle in the spacetime with a spherically symmetric black hole which is immersed in a monopole magnetic field. We show that the radial motion of the charged test particle is governed by completely the same equation as that in the case of no magnetic field. This result implies that the black hole will acquire the electric charge if it is surrounded by the collisionless plasma composed of protons and electrons which obey the Maxwell velocity distribution. The drastically different situation from no magnetic field case appears in the angular motions of charged test particles due to the magnetic field. The trajectory of a charged test particle around the black hole in the magnetic field of the order of 10 Gauss near the event horizon is confined on a very thin cone as long as the specific angular momentum of the particle is not much larger than the gravitational radius of the black hole times the speed of light. This result leads to a possibility that a plasma lump can hover over the black hole and is very hot, in the monopole magnetic field.

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Phys. Rev. D 114, 044019– Published 6 August, 2026
  • Received 1 April 2026
  • Accepted 16 July 2026
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