A model of the central engine of the unidentified high-latitude galactic hard γ-ray (EGRET) sources based on black hole electrodynamics is presented. The γ-ray emission is produced in a bipolar outflow from a charged, rotating black hole (a Kerr-Newman black hole) in a low-density region of the Galaxy, the details of which are provided in a companion paper. The model proposed in this article and its companion is a synthesis of pair creation scenarios for pulsars, the theory of black hole magnetospheres and synchrotron self-Compton large-scale jets. This article describes the physics of the putative central engine. Kerr-Newman black holes are plausible endpoints of the catastrophic gravitational collapse of the most massive magnetized rotating stars. In the following, the ability of a Kerr-Newman black hole to drive a magnetically dominated plasma wind in the charge-starved limit is explored for the first time. Although there are important analogies to magnetohydrodynamic (MHD) wind theory of Kerr (uncharged rotating) black holes, there are also enormous distinctions. However, previous experience with the MHD Kerr case is exploited to render this more complicated problem tractable. The most important parameter for quantifying the wind energy is the magnetic field line angular velocity, ΩF (and unfortunately the most difficult to calculate). The determination of ΩF is tied directly to the process by which a pair plasma is created on large-scale magnetic field lines through high-energy quantum electrodynamic processes typical of pulsar magnetospheres. It is argued in principle how ΩF is determined by the plasma injection mechanism. Furthermore, the most significant result of this effort is the calculation of ΩF for a model that is determined by a plausible set of astronomical parameters. It is essential to realize a distinction from some charge-starved pulsar models: the energy source for the wind is quantified by the field line rotation rate (the cross-field potential), ultimately powered by the rotation of the hole through dissipative gravitomagnetic processes and not the volage drop across the vacuum pair creation gap.
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