Electric charge estimation of a new-born black hole

11 pages, 1 figure, accepted to International Journal of Modern Physics DInternational audienceThough a black hole can theoretically possess a very big charge ($Q/(\sqrt{G} M) \simeq 1$), the charge of the real astrophysical black holes is usually considered to be negligible. This supposition is based on the fact that an astrophysical black hole is always surrounded by some plasma, which is a very good conductor. However, it disregards that the black holes have usually some angular momentum, which can be interpreted as its rotation of a sort. If in the plasma surrounding the hole there is some magnetic field, it leads to the electric field creation and, consequently, to the charge separation. In this article we estimate the upper limit of the electric charge of stellar mass astrophysical black holes. We have considered a new black hole formation process and shown that the charge of a new-born black hole can be significant ($\sim 10^{13}$ {Coulombs}). Though the obtained charge of an astrophysical black hole is big, the charge to mass ratio is small $Q/(\sqrt{G} M) \sim 10^{-7}$, and it is not enough to affect significantly either the gravitational field of the star or the dynamics of its collapse