On the charge of the Galactic centre black hole

2018/08/09 by Michal Zajaček, Arman Tursunov, Andreas Eckart +3 · 2 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Black Holes and Theoretical Physics #Black hole (networking) #Charge (physics) #Galactic nuclei #Galaxy #Intermediate-mass black hole #Physics #Pulsars and Gravitational Waves Research #Quantum mechanics #Stellar black hole #Supermassive black hole #astro-ph.GA #astro-ph.HE #gr-qc

paper · pdf · doi:10.1093/mnras/sty2182

17 pages, 8 figures, to be published in the MNRAS Main Journal

openalex publication_date 2018/08/09 · arxiv created 2018/08/22 · arxiv updated 2018/08/24 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05

Abstract

The Galactic centre supermassive black hole (SMBH), in sharp contrast with its complex environment, is characterized by only three classical parameters – mass, spin, and electric charge. Its charge is poorly constrained. It is, however, usually assumed to be zero because of neutralization due to the presence of plasma. We revisit the question of the SMBH charge and put realistic limits on its value, time-scales of charging and discharging, and observable consequences of the potential, small charge associated with the Galactic centre black hole. The electric charge due to classical arguments based on the mass difference between protons and electrons is |\lesssim 10⁹ \rm C| and is of a transient nature on the viscous time-scale. However, the rotation of a black hole in magnetic field generates electric field due to the twisting of magnetic field lines. This electric field can be associated with induced charge, for which we estimate an upper limit of |\lesssim 10¹⁵ \rm C|⁠. Moreover, this charge is most likely positive due to an expected alignment between the magnetic field and the black hole spin. Even a small charge of this order significantly shifts the position of the innermost stable circular orbit (ISCO) of charged particles. In addition, we propose a novel observational test based on the presence of the bremsstrahlung surface brightness decrease, which is more sensitive for smaller unshielded electric charges than the black hole shadow size. Based on this test, the current upper observational limit on the charge of Sgr A* is |\lesssim 3× 10⁸ \rm C|⁠.

Citations

• The Proper Motion of Sagittarius A*. II. The Mass of Sagittarius A*
• Black hole in a uniform magnetic field
• Viewing the Shadow of the Black Hole at the Galactic Center
• Near-infrared polarimetry setting constraints on the orbiting spot model for Sgr A* flares
• Large Mass Hierarchy from a Small Extra Dimension
• Polarimetry of near-infrared flares from Sagittarius A*
• Hot Accretion Flows Around Black Holes
• Vacuum polarization and the spontaneous loss of charge by black holes
• Relativistic images in Randall-Sundrum II braneworld lensing
• An Update on Monitoring Stellar Orbits in the Galactic Center
• Detection of intrinsic source structure at ~3 Schwarzschild radii with Millimeter-VLBI observations of SAGITTARIUS A*
• Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole

Cited by

• Silhouettes of invisible black holes
• Innermost stable circular orbit of charged particles in Reissner-Nordström, Kerr-Newman, and Kerr-Sen spacetimes