We present improved estimates of the electric charge that black holes could hold when these are embedded in the ionised plasma within galaxies. We have implemented the spontaneous emission of charges of opposite sign to that of the black hole via athermal Hawking evaporation, including its dependence on black hole spin, and we have estimated the equilibrium charge that arises as this charge loss is balanced by the continuous accretion of charges from the surrounding plasma. The resulting charge can be several orders of magnitude lower than previously estimated upper limits, but it can surpass the pair production limit noted by Gibbons (1974) by a margin that increases with the amplitude of the black hole spin and the density of the plasma. We also implement a calculation for the net charge of galaxies due to their stellar black holes and to primordial black holes in the case these make up a fraction of the dark matter. We find that these charges lie within the range that would produce adequate magnetic field seeds at the onset of galaxy formation.

中文翻译：

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星系内黑洞的电荷

当黑洞嵌入星系内的电离等离子体中时，我们对黑洞可能持有的电荷提出了改进的估计。我们通过非热霍金蒸发实现了与黑洞符号相反的电荷的自发发射，包括其对黑洞自旋的依赖性，并且我们估计了当这种电荷损失通过不断吸积来平衡时产生的平衡电荷。来自周围等离子体的电荷。由此产生的电荷可能比之前估计的上限低几个数量级，但它可以超过 Gibbons (1974) 指出的对产生极限，其幅度随着黑洞自旋幅度和等离子体密度的增加而增加。我们还对星系的净电荷进行了计算，因为它们的恒星黑洞和原初黑洞构成了暗物质的一小部分。我们发现这些电荷位于星系形成开始时产生足够磁场种子的范围内。