Publication date: Dec 2018
Abstract:
In this contribution, we summarize our results concerning the
observational constraints on the electric charge associated with the
Galactic centre black hole – Sgr A*. According to the no-hair theorem,
every astrophysical black hole, including supermassive black holes, is
characterized by at most three classical, externally observable
parameters – mass, spin, and the electric charge. While the mass and the
spin have routinely been measured by several methods, the electric
charge has usually been neglected, based on the arguments of efficient
discharge in astrophysical plasmas. From a theoretical point of view,
the black hole can attain charge due to the mass imbalance between
protons and electrons in fully ionized plasmas, which yields about $sim
10^8,{rm C}$ for Sgr A*. The second, induction mechanism concerns
rotating Kerr black holes embedded in an external magnetic field, which
leads to electric field generation due to the twisting of magnetic field
lines. This electric field can be associated with the induced Wald
charge, for which we calculate the upper limit of $sim 10^{15},{rm
C}$ for Sgr A*. Although the maximum theoretical limit of $sim
10^{15},{rm C}$ is still 12 orders of magnitude smaller than the
extremal charge of Sgr A*, we analyse a few astrophysical consequences
of having a black hole with a small charge in the Galactic centre. Two
most prominent ones are the effect on the X-ray bremsstrahlung profile
and the effect on the position of the innermost stable circular orbit.
Authors:
Zajaček, Michal; Tursunov, Arman; Eckart, Andreas; Britzen, Silke; Hackmann, Eva; Karas, Vladimír; Stuchlík, Zdeněk; Czerny, Bozena; Zensus, J. Anton;