Internal instabilities in magnetized jets

Abstract

We carry out an extensive linear stability analysis of magnetized cylindrical jets in a global framework. Foregoing the commonly invoked force-free limit, we focus on the small-scale, internal instabilities triggered in regions of the jet dominated by a toroidal magnetic field, with a weak vertical field and finite thermal pressure gradient. Such regions are likely to occur far from the jet source and boundaries, and are potential sites of magnetic energy dissipation that is essential to explain the particle acceleration and radiation observed from astrophysical jets. We validate the local stability analysis of Begelman by verifying that the eigenfunctions of the most unstable modes are radially localized. This finding allows us to propose a generic stability criterion in the presence of a weak vertical field. A stronger vertical field with a radial gradient complicates the stability criterion, due to the competition between the destabilizing thermal pressure gradient and stabilizing magnetic pressure gradients. Nevertheless, we argue that the jet interiors generically should be subject to rapidly growing, small-scale instabilities, capable of producing current sheets that lead to dissipation. We identify some new instabilities, not predicted by the local analysis, which are sensitive to the background radial profiles but have smaller growth rates than the local instabilities, and discuss the relevance of our work to the findings of recent numerical jet simulations.

On the significance of relativistically hot pairs in the jets of FR II radio galaxies

“…At distance scales larger than tens of parsecs, the radiative cooling of even ultra-relativistic electrons is inefficient, and in order to maintain the energy flux of pairs, the required heating rate is determined mainly by the need to compensate the adiabatic losses (Potter, & Cotter 2015;Zdziarski et al 2019). Such heating can be mediated by the oblique/reconfinement shocks, which regulate the pressure balance between the jet and its environment, and are predicted to stimulate the kink instabilities followed by a variety of particle acceleration mechanisms (e.g., Tchekhovskoy, & Bromberg 2016;Barniol Duran et al 2017;Alves et al 2018;Das, & Begelman 2019). Since the formation of such shocks requires the upstream flow to be supersonic, we can expect them to become weaker when the energy flux carried by the pairs starts to dominate over the energy flux carried by the 'cold' protons.…”

Kinetic turbulence in shining pair plasma: intermittent beaming and thermalization by radiative cooling

“…where L turb (r) represents the size of a turbulent region inside the jet, presumably driven by internal instabilities such as the kink mode (Begelman 1998;Das & Begelman 2019). For the sake of argument, if we assume L turb ∼ 0.1r/Γj and ηinj ∼ 0.1, then from Eq.…”

Study of particle acceleration by magnetic reconnection in relativistic jets

“…The presence of instabilities in the jet can drive turbulence and thus fast magnetic reconnection (e.g., Spruit et al, 2001;Barniol Duran et al, 2017;de Gouveia Dal Pino et al, 2018;Gill et al, 2018). In particular, jets with helical magnetic field structure can be subject to the current-driven kink (CDK) instability (e.g., Begelman, 1998;Giannios and Spruit, 2006;Mizuno et al, 2009Mizuno et al, , 2011Mizuno et al, , 2012Mizuno et al, , 2014Das and Begelman, 2019).…”

“…It is known, from theory and laboratory experiments of plasma physics that cylindrical, magnetized plasmas are unstable to various kinds of instabilities (Bateman, 1978;Hsu and Bellan, 2002;Bellan et al, 2005;Moser and Bellan, 2012). In magnetized outflows, the instabilities can be driven by two classes, pressure-driven and current-driven instabilities (Das and Begelman, 2019). Pressure-driven instability is induced by the electric current perpendicular to the magnetic field (j ⊥ ) and by the interaction between the pressure of the gas and the magnetic tension of the magnetic field lines, and the instability occurs when the plasma pressure gradient is strong enough to push the plasma out of the curvature of magnetic field lines.…”

“…the CDKI, because it affects the jet axis, and its center of mass changes into a spiral shape. For all other values of |m|, the center of mass remains on the axis and the perturbations are concentrated on the outside (see for more details on this instability Bateman, 1978;Begelman, 1998;Lyubarskii, 1999;Hardee, 2004;Braithwaite, 2006;Narayan et al, 2009;Das and Begelman, 2019).…”