Disk-Jet Coupling in Black Hole Accretion Systems I: Order within Chaos

General relativistic numerical simulations of magnetized accretion flows around black holes show accreting gas with chaotic motions at equatorial latitudes and coronae and outflows with chaotic magnetic field at higher latitudes. However, the same simulations also produce highly relativistic, Poynting-dominated jets that are nearly consistent with the stationary paraboloidal Blandford-Znajek model of an organized field threading the polar regions of a rotating black hole. How can a disordered accretion disk and corona lead to an ordered jet? We show that the accretion disk and corona, despite appearing very disordered, have a strikingly simple toroidal current distribution of the form dIφ/dr ∝ r , where Iφ(r) is the toroidal current enclosed inside radius r. We demonstrate that the poloidal magnetic field in the jet agrees well with the force-free field solution for a non-rotating equatorial current sheet with the r current distribution, thus confirming a close causal relationship between the simple current seen in the numerically simulated disk and the ordered field in the jet. The r current is associated with an r dependence of the field strength in the disk, which is similar to the scaling assumed in two accretion/outflow models in the literature: the magnetohydrodynamic disk wind model of Blandford & Payne (1982) and the advection-dominated accretion flow model of Narayan & Yi (1995). However, the agreement is accidental since these models assume Newtonian gravity and equipartition between magnetic and gas pressure, neither of which is valid in the numerical model.