Extracting Energy Magnetically From Black Hole Accretion Disk Through Plunging Region

In this thesis, three mechanisms of extracting energy magnetically from black hole-accretion disc (the BZ, MC and DL process) are investigated in detail based on the theories of magnetosphere and equivalent circuit, and some important applications to high-energy astrophysics are discussed as well. In addition, a toy model for magnetic extraction of energy from the plunging region by the large-scale magnetic field is proposed. The main results are summarized as follows.Firstly, the analytical expressions for the electromagnetic powers and torques are derived by using an improved equivalent circuits corresponding to the three energy mechanisms, and a reasonable mapping relation and the co-rotation radius are discussed in the MC process.Secondly, we discuss some important applications to astrophysics: By virtue of the BZ mechanism, we fit the jet powers observed in some BH X-ray binaries. The MC process can be used to explain a very steep emissivity in the inner region of the disc, which is consistent with the recent observations of the nearby Seyfert I galaxy MCG-6-30-15. It turns out that the jet powers of quasars can be well fitted by the DL power given in this thesis.Thirdly, the jet power extracted by a large-scale magnetic field from the plunging region is investigated, and the analytical expression for the jet power is derived based an improved equivalent circuit. Furthermore,the relative importance of the PL, BZ and DL powers is compared in detail. It is shown that the PL power is stronger than the BZ and DL powers especially for the slow-spinning black hole (BH), and we use the PL power derived in our model to fit the strong jet powers of several 3CR FR I radio galaxies. In addition, the condition for the negative energy in the plunging region is discussed with the validity of the second law of BH thermodynamics.Fourthly, the magnetic coupling of the plunging region with the disc is investigated based on a large-scale magnetic field configuration (henceforth MCPD). We calculate the power and torque in MCPD by using an improved equivalent circuit, and compare with another magnetic coupling of the BH with the disc (henceforth MCHD). It is shown that MCPD is generally more important than MCHD in transferring energy and angular momentum to the disc for low BH spins. In addition, we discuss the condition of the negative energy of the plunging particles by considering the accretion rate affected by MCPD and the validity of the second law of BH thermodynamics.Finally, we summarize the main results and point out the aspects that need to be improved in the future.