Vladimir Ivanovich Pariev

A Magnetic α-ω Dynamo in AGN Disks. II. Magnetic Field Generation, Theories, and Simulations

It is shown that a dynamo can operate in an Active Galactic Nuclei (AGN) accretion disk due to the Keplerian shear and due to the helical motions of expanding and twisting plumes of plasma heated by many star passages through the disk. Each plume rotates a fraction of the toroidal flux into poloidal flux, always in the same direction, through a finite angle, and proportional to its diameter. The predicted growth rate of poloidal magnetic flux, based upon two analytic approaches and numerical simulations, leads to a rapid exponentiation of a seed field, ∼ 0.1 to ∼ 0.01 per Keplerian period of the inner part of the disk. The initial value of the seed field may therefore be arbitrarily small yet reach, through dynamo gain, saturation very early in the disk history. Because of tidal disruption of stars close to the black hole, the maximum growth rate occurs at a radius of about 100 gravitational radii from the central object. The generated mean magnetic field, a quadrupole field, has predominantly even parity so that the radial component does not reverse sign across the midplane. The linear growth is predicted to be the same by each of the following three theoretical analyses: the flux conversion model, the mean field approach, and numerical modeling. The common feature is the conducting fluid flow, considered in companion Paper I (Pariev & Colgate 2006) where two coherent large scale flows occur naturally: the differential winding of Keplerian motion and differential rotation of expanding plumes.

A Magnetic α-ω Dynamo in AGN Disks. I. The Hydrodynamics of Star-Disk Collisions and Keplerian Flow

A magnetic field dynamo in the inner regions of the accretion disk surrounding the supermassive black holes in Active Galactic Nuclei (AGNs) may be the mechanism for the generation of magnetic fields in galaxies and in extragalactic space. We argue that the two coherent motions produced by 1) the Keplerian motion and 2) star-disk collisions, numerous in the inner region of AGN accretion disks, are both basic to the formation of a robust, coherent dynamo and consequently the generation of large scale magnetic fields. In addition we find that the predicted rate, 10 to 100 per year at ∼ 1000rg, rg the gravitational radius, and the consequences of star-disk collisions are qualitatively, at least, not inconsistent with observations of broad emission and absorption lines. They are frequent enough to account for an integrated dynamo gain, e 10 9 at 100rg, many orders of magnitude greater than required to amplify any seed field no matter how small. The existence of extra-galactic, coherent, large scale magnetic fields whose energies greatly exceed all but massive black hole energies is recognized. In paper II (Pariev, Colgate & Finn 2006) we argue that in order to produce a dynamo that can access the free energy of black hole formation and produce all the magnetic flux in a coherent fashion the existence of these two coherent motions in a conducting fluid is required. The differential winding of Keplerian motion is obvious, but the disk structure depends upon the model of ”α”, the transport coefficient of angular momentum chosen. The counter rotation of driven plumes in a rotating frame is less well known, but fortunately the magnetic effect is independent of the disk model. Both motions are discussed in this paper, paper I. The description of the two motions are preliminary to two theoretical derivations and one numerical simulation of the αω dynamo in paper II.

The origin of the magnetic fields of the universe: The plasma astrophysics of the free energy of the universe

The largest accessible free energy in the universe is almost certainly the binding energy of the massive central black hole (BH) of nearly every galaxy. We have calculated one mechanism that produces this characteristic mass, 108M⊙, by initiating a Rossby vortex dominated accretion disk at a critical thickness, ∼100 g cm−2, in the development of the flat rotation curve of nearly every galaxy. We have simulated how an α-Ω dynamo should work due to star-disk collisions and plume rotation. The back reaction of this saturated dynamo may convert almost all the accretion energy into a single force-free magnetic field helix. This helix and field energy is then distributed as a quasi-static, hydrodynamically stable, Poynting flux configuration, filling the intergalactic space with a magnetized plasma. This energy and flux also explains the Faraday rotation maps of AGN in clusters. This energy density is ∼103 times the virial energy of a galactic mass of baryonic matter in the combined gravity of dark and baryonic...