Effects of the Blandford-Znajek Process on Evolution of Radial Structure of Black Hole Accretion Disks

  • D. X. Wang
Part of the Astrophysics and Space Science Library book series (ASSL, volume 254)


It is well known that the Blandford-Znajek (BZ) process is an effective mechanism for extracting rotating energy and angular momentum of a central black hole (BH) surrounded by accretion disk (Blandford & Znajek 1977; Macdonald & Thorne 1982 henceforth MT). The BZ extracting mechanism always works together with accretion of matter onto BHs: Leaving the inner edge of the accretion disk, the disk plasma gradually spirals and carries its frozen-in magnetic field onto the BH horizon. The strength of the BZ process depends crucially on the strength of the magnetic field, B⊥, normal to the BH horizon. Recently, it was pointed out that the values of B⊥ were overestimated substantially in previous works, and the BZ extracting power (hereafter the BZ power) is not as strong as imagined previously (Ghosh & Abramowitz 1997; Livio, Ogilvie & Pringle 1999). The overestimate of B⊥ arises from the incomplete argument on the BZ process, in which the Maxwell pressure, B 2 /8π, was assumed to correspond to an equilibrium with the maximum total pressure in the inner parts of the accretion disk rather than the Maxwell pressure near the inner edge. The modified BZ powerPin radiation-pressure dominated case can be expressed as (Wang 1999a):
$$P = (4/65)k(1 - k)a_ \star ^2{E_{in}}{M_0}$$
Eq.(l) will be used to investigate the effects of the BZ process on the evolution of the radial structure of BH accretion disks in this paper.


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Copyright information

© Springer Science+Business Media Dordrecht 2000

Authors and Affiliations

  • D. X. Wang
    • 1
  1. 1.Department of PhysicsHuazhong University of Science and TechnologyWuhanChina

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