Sustained Magnetic Fields Over Astrophysical Scale Distances

Considering the plasma disk associated with a binary system made of two black holes, one of them at least can carve a “Swept Torus” [1,2], a region encompassing the binary that is emptied by the BH passage. Ion-sound modes involving both electron temperature and density fluctuations can emerge and, as shown in Ref. [1], propagate in pairs of coupled modes as double-helix structures. In the presence of a finite electron viscosity or of a finite electrical resistivity, that is of a finite magnetic field diffusion coefficient, a long wave nearly stationary magnetic field is shown to be produced by the paired density and temperature fluctuations (a “Cosmic Dynamo”). Another non linear process that is proposed involves ion-sound modes that can reach sufficient amplitudes to alter [3} the electron distribution in momentum space and produce a multi component pressure tensor. Then magnetic field fluctuations became associated with the sustained mode [4]. This process (a “Cosmic Alternator”) [5] would generate a slowly varying magnetic field. Thus further analysis is suggested where density fluctuations would couple non linearly with a component of the electron pressure tensor [5] and where a finite electron viscosity or magnetic field diffusion coefficient is included. The purpose of this is to produce a nearly stationary field.

[1] B. Coppi, Fundamental Plasma Physics 4, 100007 (2023).

[2] B. Coppi, Invited Papers for the XVI M. Grossmann Conference on Astrophysics (Session I), July 2021, and for the Asia Pacific Conference on Plasma Physics (SA-118), October 2021.

[3] S. Ashwin, P. Kumar, A.C. Fletcher, et al. Phys. Plasmas 32, 022103 (2025)

[4] B. Coppi and P.S. Coppi, Asia Pacific Conference on Plasma Physics (SA-118), October 2021.

[6] B. Coppi and B. Basu, Phys. Plasmas 32, 022103 (2025).