Propagation and stability of relativistic jets

TL;DR

This paper reviews the mechanisms behind the formation, propagation, and dissipation of relativistic jets from compact objects, highlighting differences between types and scales, and proposing models for energy dissipation and particle acceleration.

Contribution

It provides a comprehensive overview of jet formation, stability, and dissipation mechanisms, including new expressions for entrainment distances in FRI jets and comparisons across different astrophysical contexts.

Findings

Identification of key dissipation mechanisms such as MHD instabilities and shocks.

Derivation of an expression for entrainment distance in FRI jets.

Discussion of evolutionary differences between extragalactic and microquasar jets.

Abstract

A simple look at the steady high-energy Universe reveals a clear correlation with outflows generated around compact objects (winds and jets). In the case of relativistic jets, they are thought to be produced as a consequence of the extraction of rotational energy from a Kerr black hole (Blandford-Znajek), or from the disc (Blandford-Payne). A fraction of the large energy budget provided by accretion and/or black hole rotational energy is invested into jet formation. After formation, the acceleration and collimation of these outflows allow them to propagate to large distances away from the compact object. The synchrotron cooling times demand that re-acceleration of particles takes place along the jets to explain high-energy and very-high-energy emission from kiloparsec scales. At these scales, jets in radio galaxies are divided in two main morphological/luminosity types, namely, Fanaroff-Riley type I and II (FRI, FRII), the latter being more luminous, collimated and edge-brightened than the former, which show clear hints of decollimation and deceleration. In this contribution, I summarise a set of mechanisms that may contribute to dissipate magnetic and kinetic energy: Magnetohydrodynamic instabilities or jet-obstacle interactions trigger shocks, shearing and mixing, which are plausible scenarios for particle acceleration. I also derive an expression for the expected distance in which the entrainment by stellar winds starts to be relevant, which is applicable to FRI jets. Finally, I discuss the differences in the evolutionary scenarios and the main dissipative mechanisms that take place in extragalactic and microquasar jets.