Direct measurements of black hole charge with future astrometrical missions

¹ National Astronomical Observatories of Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, PR China
² Institute of Theoretical and Experimental Physics, 25 B. Cheremushkinskaya st., Moscow 117259, Russia e-mail: zakharov@itep.ru
³ Astro Space Centre of Lebedev Physics Institute, 84/32, Profsoyuznaya st., Moscow 117810, Russia
⁴ Joint Institute for Nuclear Research, Dubna, Russia
⁵ Department of Physics, University of Lecce and INFN, Section of Lecce, via Arnesano, 73100 Lecce, Italy

Received: 13 May 2005
Accepted: 26 July 2005

Abstract

Recently, Zakharov et al. (2005a, New Astron., 10, 479) considered the possibility of evaluating the spin parameter and the inclination angle for Kerr black holes in nearby galactic centers by using future advanced astrometrical instruments. A similar approach which uses the characteristic properties of gravitational retro-lensing images can be followed to measure the charge of a Reissner-Nordström black hole. Indeed, in spite of the fact that their formation might be problematic, charged black holes are objects of intensive investigations. From a theoretical point of view, it is well-known that a black hole is described by only three parameters, namely, its mass M, angular momentum J, and charge Q. Therefore, it would be important to have a method for measuring all these parameters, preferably by independent model of any. In this paper, we propose a procedure to measure the black hole charge by using the size of the retro-lensing images that can be revealed by future astrometrical missions. A discussion of the Kerr-Newmann black hole case is also offered.