Thermodynamic evolution of the central black hole of active galactic nuclei

Under the combined effect of accretion and the Blandford-Znajek process, th e dimensionless angular momentum of the central black hole in AGNe grows to a stable value below that for the extreme Kerr black hale, so the third la w of black hole thermodynamics is not violated. The stable value exists-for both thin and thick disks; its size is determined by the strength of the B -Z process and the disk geometry and is independent of the black hole mass or the accretion rate.