# The remarkable AGN jets

## TL;DR

This paper explores why AGN jets are remarkably stable over vast distances, attributing it mainly to environmental factors like rapid density decline that suppress instabilities, and discusses implications for jet classification and dynamics.

## Contribution

It provides a detailed analysis of environmental influences on AGN jet stability and examines the connection with Fanaroff-Riley classification, highlighting the role of external pressure profiles.

## Key findings

- AGN jets can propagate over billion-scale distances due to environmental expansion effects.
- External pressure decline suppresses global instabilities in jets.
- Observations challenge simple models of jet causal connectivity.

## Abstract

The jets from active galactic nuclei exhibit stability which seems to be far superior compared to that of terrestrial and laboratory jets. They manage to propagate over distances up to a billion of initial jet radii. Yet this may not be an indication of some exotic physics but mainly a reflection of the specific environment these jets propagate through. The key property of this environment is a rapid decline of density and pressure along the jet, which promotes its rapid expansion. Such an expansion can suppress global instabilities, which require communication across the jet, and hence ensure its survival over huge distances. At kpc scales, some AGN jets do show signs of strong instabilities and even turn into plumes. This could be a result of the flattening of the external pressure distribution in their host galaxies or inside the radio lobes. In this regard, we discuss the possible connection between the stability issue and the Fanaroff-Riley classification of extragalactic radio sources. The observations of AGN jets on sub-kpc scale do not seem to support their supposed lack of causal connectivity. When interpreted using simple kinematic models, they reveal a rather perplexing picture with more questions than answers on the jets dynamics.