Abstract
Observed correlations between the disk luminosity (L) and radio emission from accreting black hole (BH) systems indicate underlying couplings between BH accretion disk and jet. Assuming relativistic jets are launched at the expense of the rotational energy of spinning BHs, we examine whether the BH energy can be extracted outward when the accretion disk type varies with L/LEdd, where LEdd is the Eddingtion luminosity. In this thesis, we mainly focus on why relativistic jet is launched before the disk is dominated by the thin disk type (before L/LEdd approaches the value ∼ 0.01), as inferred from observation. Considering the general relativistic magnetohydrodynamics (MHD), we found the extraction of BH energy via the “MHD Penrose process” (and hence the relativistic jet)can preferentially take place when the BH is surrounded by a disk which consists a (outer) thin disk and an (inner) advection-dominated flow. Such combined disk has been inferred from the spectra of both BH X-ray binaries and active galactic nuclei. Our model also consistently explains why both the radio luminosity and jet speed increase with increasing X-ray luminosity. In addition, we propose possible explanations why jet are quenched at when L/LEdd ∼ 0.01 and why the jets launched when L/LEdd > 0.01 has different jet power and jet speed than those launched when L/LEdd < 0.01. It is suggested that, for different types of accretion disks, both the transonic flow geometry near the horizon, and the large–scale magnetic field confined by the disk, play essential roles in affecting the extraction of BH rotational energy and hence the jet formation.