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302 6 MACRO– AND MICRO–JETS DRIVEN BY BLACK HOLES process is the strength of the poloidal magnetic field. The standard approach (e.g., Moderski & Sikora 1996) to estimating BH is to set it equal to Bφ, the dominant azimuthal magnetic field component given by the disk structure equations, yielding and Ljet,B = 2 × 10 45 erg s −1 m9 ˙m−2 j 2 (726) Ljet,A = 3 × 10 49 erg s −1 m 0.8 9 ˙m−1 j 2 . (727) for Class B (radio galaxy/ADAF) and Class A (quasar/standard disk) objects, respectively. Note that, while the jet is not accretion-powered in this model, the efficiency of extraction is still essentially linear in ˙m. Basic physics of MHD acceleration and collimation: Though many models have been proposed to generate jets, the magnetohydrodynamic (MHD) model is still the leading one (Fig. 145). In this picture, the plasma is simplified in terms of a one– component approximation and the conductivity is assumed to be very high so that electric fields in the plasma are shorted out. In a first approximation, plasma is not allowed to cross field lines, it can only flow parallel to them. In regions where the field is weak or the plasma is dense, the rotating field will be bent backward. To accelerate and collimate a jet with magnetic fields, all that is needed is a gravitating body to collect the material which should be ejected, a poloidal magnetic field threading that material, and some differential rotation, which produces a helical structure in the field. This rotating field structure drives the confined plasma upwards and outwards along the field lines. As this twist propagates outwards, the toroidal field pinches the plasma towards the rotational axis. Depending on the relative importance of the magnetic field, the plasma density and rotation, a variety of configurations are possible from spherical winds, slowly collimated and highly collimated outflows. Poloidal magnetic field strengths are estimated from equation disk pressure, but (H/R) is of order unity for the low cases, and also for the high Kerr case due to Lens-Thirring bloating of the inner disk. Otherwise (H/R) is calculated from the electron scattering/gas pressure disk model of Shakura & Sunyaev (1973), and disk field strengths are computed from that paper or from Narayan et al. (1998), as appropriate. The logarithms of the resulting poloidal field strengths, and corresponding jet powers, are represented as field line and jet arrow widths. In the Kerr cases, the inner disk magnetic field is significantly enhanced over the Schwarzschild cases, due in part to the smaller last stable orbit (flux conservation) and in part to the large (H/R) of the bloated disks. The high accretion rate, Schwarzschild case has the smallest field - and the weakest jet - because the disk is thin, the last stable orbit is relatively large, and the Keplerian rotation rate of the field there is much smaller than it would be in a Kerr hole ergosphere. Enhancement of the poloidal field due to the buoyancy process suggested by Krolik (1999) is ignored here because we find
6.7 Formation of Micro–Jets 303 Figure 145: Essential elements for magnetic jet formation. A torus of hot gas is initially magnetized by vertical magnetic fields. The differential rotation of the torus drags the field lines in the azimuthal direction, angular momentum is thereby carried away from the disk material which allows the material to accrete inwards towards the horizon. This exerts a torque on the external field with a kind of torsional Alfvèn wave. This carries away angular momentum and energy from the system. [Meier et al., Science 291 (2001)].
Page 1 and 2: CONTENTS 265 Contents 6 Macro- and
Page 3 and 4: 6 Macro- and Micro-Jets Driven by B
Page 5 and 6: 6.1 DRAG(o)Ns - FR I and FR II 269
Page 11 and 12: 6.2 Jets as Super(magneto)sonic Col
Page 13 and 14: 6.2 Jets as Super(magneto)sonic Col
Page 15 and 16: 6.3 Fundamental Parameters for Jets
Page 17 and 18: 6.3 Fundamental Parameters for Jets
Page 19 and 20: 6.4 A 3-Phase Model for Kiloparsec-
Page 25 and 26: 6.5 Relativistic Jet Propagation 28
Page 27 and 28: 6.6 Structure and Emission of Micro
Page 37: 6.7 Formation of Micro-Jets 301 6.7
Page 41 and 42: 6.7 Formation of Micro-Jets 305 Thi
Page 43 and 44: 6.7 Formation of Micro-Jets 307 VLB
Page 45 and 46: 6.7 Formation of Micro-Jets 309 as
Page 47 and 48: 6.7 Formation of Micro-Jets 311 Fig
Page 53 and 54: 6.7 Formation of Micro-Jets 317 the
Page 55 and 56: 7.1 The Dark Age 319 Figure 152: Da
Page 57 and 58: 7.3 The First Quasars 321 Figure 15
Page 59 and 60: 7.3 The First Quasars 323 Bromm & L
Page 61: REFERENCES 325 [17] Leahy, P. 1993,

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