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An Introduction to Particle Acceleration in Shearing Flows

1
ZAH, Institut für Theoretische Astrophysik, Heidelberg University, Philosophenweg 12, 69120 Heidelberg, Germany
2
Max-Planck-Institut für Kernphysik, P.O. Box 103980, 69029 Heidelberg, Germany
Galaxies 2019, 7(3), 78; https://doi.org/10.3390/galaxies7030078
Received: 15 August 2019 / Revised: 5 September 2019 / Accepted: 6 September 2019 / Published: 10 September 2019
(This article belongs to the Special Issue Particle Acceleration Processes in Astrophysical Jets)
Shear flows are ubiquitously present in space and astrophysical plasmas. This paper highlights the central idea of the non-thermal acceleration of charged particles in shearing flows and reviews some of the recent developments. Topics include the acceleration of charged particles by microscopic instabilities in collisionless relativistic shear flows, Fermi-type particle acceleration in macroscopic, gradual and non-gradual shear flows, as well as shear particle acceleration by large-scale velocity turbulence. When put in the context of jetted astrophysical sources such as Active Galactic Nuclei, the results illustrate a variety of means beyond conventional diffusive shock acceleration by which power-law like particle distributions might be generated. This suggests that relativistic shear flows can account for efficient in-situ acceleration of energetic electrons and be of relevance for the production of extreme cosmic rays. View Full-Text
Keywords: shearing flows; relativistic outflows; AGN jets; particle transport; acceleration shearing flows; relativistic outflows; AGN jets; particle transport; acceleration
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Rieger, F.M. An Introduction to Particle Acceleration in Shearing Flows. Galaxies 2019, 7, 78.

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