Black-hole Accretion Disc And Jets Of Active Galactic Nuclei

Two types of mechanisms of extracting energy from a rotating black hole by magnetic field, the Blandford-Znajek (BZ) process and magnetic coupling (MC) process, are investigated in detail based on the theory of the black hole magnetosphere, and the electromagnetic model for jet power extracted from the inner region of the accretion disc by large scaled magnetic field is proposed in this thesis. The main results are summarized as follows. Firstly, the unified analytical expressions for the BZ and MC powers and torques are derived based an improved equivalent circuit, and the condition for the coexistence of the BZ process and the MC process are discussed. In addition, we find that the very steep emissivity produced the MC process is consistent with the recent observations of the nearby Seyfert I galaxy MCG-6-30-15. Secondly, the Poynting jet launched by a large scaled magnetic field from the standard thin disc is investigated, and the analytical expression for the jet power is derived. Furthermore, our result is compared with some author's results. It is found that a large fraction of the jet power is contributed from the inner region of the disc. In addition, the relative importance of this jet power to the BZ power is discussed. It is shown that the BZ power is generally dominated by the jet power except in some extreme cases. Thirdly, an electromagnetic jet model for jet power extracted from an advection dominated accretion flow (ADAF) is proposed, and the analytical expression for this jet power an torque is derive by using an equivalent circuit. Our result demonstrates that the jet power concentrates on the inner region more than it in the case of the standard thin disc, and the jet power depends sensitively on the degree to which the flow is advection-dominated. Finally, we use the jet powers extracted from the standard thin disc and ADAF to fit the jet powers of quasars and BL Lac objects in this thesis.