The Origin of the Magnetic Fields of the Universe: The Plasma Astrophysics of the Free Energy of the Universe

Research paper by S. A. Colgate, H. Li, V. Pariev

Indexed on: 22 Dec '00Published on: 22 Dec '00Published in: Astrophysics


(abridged) The interpretation of Faraday rotation measure maps of AGNs within galaxy clusters has revealed regions, $\sim 50-100$ kpc, that are populated with large, $\sim 30 \mu$ G magnetic fields. The magnetic energy of these coherent regions is $\sim 10^{59-60}$ ergs, and the total magnetic energy over the whole cluster ($\sim 1$ Mpc across) is expected to be even larger. A sequence of physical processes that are responsible for the production, redistribution and dissipation of these magnetic fields is proposed. These fields are associated with single AGNs within the cluster and therefore with all galaxies during their AGN phase, simply because only the central supermassive black holes ($\sim 10^8 M_{\odot}$) have an accessible energy, $\sim 10^{61}$ ergs. We propose an $\alpha-\Omega$ dynamo process in an accretion disk. The disk rotation naturally provides a large winding number, $\sim 10^{11}$ turns, sufficient to make both large gain and large flux. The helicity of the dynamo can be generated by the differential plume rotation derived from star-disk collisions. This helicity generation process has been demonstrated in the laboratory and the dynamo gain was simulated numerically. A liquid sodium analog of the dynamo is being built. Speculations are that the back reaction of the saturated dynamo will lead to the formation of a force-free magnetic helix, which will carry the energy and flux of the dynamo away from the accretion disk and redistribute the field within the clusters and galaxy walls. The magnetic reconnection of a small fraction of this energy logically is the source of the AGN luminosity, and the remainder of the field energy should then dominate the free energy of the present-day universe.