In Situ Magnetic Field Generation and Plasma Structures as Constituents of Astrophysical Jets

Ion acoustic modes [1] are shown to cease being electrostatic, contrary to what is commonly assumed [2], and to have finite magnetic fields associated with them when the relevant fluctuating electron distribution (in momentum space) is not a Maxwellian and the resulting electron pressure tensor is not isotropic. This finding is used to advance the theory of the plasma structures that were proposed [3] to be the constituents of astrophysical jets. In fact, these structures had been associated with ion-acoustic modes emerging from the “swept torus” [1] in the circumbinary disk sustained by a pair of black holes. The observed magnetic field filaments [4, 5] characterizing these structures are explained as resulting from long wavelength magnetic field strings [6] sustained by slowly evolving and large amplitude ion-acoustic electromagnetic modes. An option that does not require the formation of a non-Maxwellian electron distribution, is the generation of a slowly varying magnetic field by the non-linear coupling [1] of modes involving density and electron temperature slow fluctuations, a special case of a “Cosmic Alternator” [6]. When a finite electron viscosity process is included, a nearly stationary field can emerge from this coupling, and this can be referred to as a “Cosmic Dynamo”.

[1] B. Coppi, Fundamental Pl. Phys. 100007 (2023).

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

[3] 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.

[4]. A. Pasetto et al., Ap J. Letters, 923:L5 (2021).

[5] G-Y. Zhao, Ap J., et al., 932:73 (2022).

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