Clouds and red giants interacting with the base of AGN jets

TL;DR

This study uses relativistic hydrodynamical simulations to explore how interactions between gas clouds or red giant atmospheres and the base of AGN jets can lead to jet mass-loading, particle acceleration, and gamma-ray emission.

Contribution

It provides the first detailed relativistic hydrodynamical simulations of obstacle interactions at the jet base, highlighting their effects on jet dynamics and high-energy phenomena.

Findings

Obstacles expand and disrupt inside the jet, contributing to mass-loading.

Inhomogeneous obstacles can form a dense core, affecting disruption timescales.

Interactions can produce variable gamma-ray emission and jet slowing.

Abstract

Extragalactic jets are formed close to supermassive black-holes in the center of galaxies. Large amounts of gas, dust, and stars cluster in the galaxy nucleus, and interactions between this ambient material and the jet base should be frequent, having dynamical as well as radiative consequences. This work studies the dynamical interaction of an obstacle, a clump of matter or the atmosphere of an evolved star, with the innermost region of an extragalactic jet. Jet mass-loading and the high-energy outcome of this interaction are briefly discussed. Relativistic hydrodynamical simulations with axial symmetry have been carried out for homogeneous and inhomogeneous obstacles inside a relativistic jet. These obstacles may represent a medium inhomogeneity or the disrupted atmosphere of a red giant star. Once inside the jet, an homogeneous obstacle expands and gets disrupted after few dynamical timescales, whereas in the inhomogeneous case, a solid core can smoothen the process, with the obstacle mass-loss dominated by a dense and narrow tail pointing in the direction of the jet. In either case, matter is expected to accelerate and eventually get incorporated to the jet. Particles can be accelerated in the interaction region, and produce variable gamma-rays in the ambient matter, magnetic and photon fields. The presence of matter clumps or red giants into the base of an extragalactic jet likely implies significant jet mass-loading and slowing down. Fast flare-like gamma-ray events, and some level of persistent emission, are expected due to these interactions.