Relativistic hydrodynamics simulations of supernova explosions within extragalactic jets

¹ Departament d’Astronomia i Astrofísica, Universitat de València, C/ Dr. Moliner, 50, 46100 Burjassot, València, Spain
² Observatori Astronòmic, Universitat de València, C/ Catedràtic José Beltrán 2, 46980 Paterna, València, Spain
³ Departament de Fìsica Quàntica i Astrofísica, Institut de Ciències del Cosmos (ICC), Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, E08028 Barcelona, Spain

^★ Corresponding author: bruno.longo@uv.es

Received: 6 June 2025
Accepted: 6 October 2025

Abstract

Context. Jets in active galactic nuclei (AGN) have to cross significant distances within their host galaxies, meeting large numbers of stars of different masses and evolution stages on their paths. Given enough time, supernova explosions within the jet will eventually happen, and they may have a strong impact on its dynamics, potentially triggering powerful non-thermal activity.

Aims. We aim to carry out a detailed numerical study to explore the dynamics of the interaction between the ejecta of a supernova explosion and a relativistic extragalactic jet.

Methods. By means of relativistic hydrodynamics simulations using the code RATPENAT, we simulated the jet-ejecta interaction in two different geometries or scenarios: a two-dimensional, axisymmetric simulation, and a three-dimensional one, which includes the orbital velocity of the exploding star. In both scenarios, the supernova ejecta is located within the jet at a distance of ∼1 kpc from the central black hole, which is the spatial scale on which these events are most likely.

Results. Although initially filling a region much smaller than the jet radius, the ejecta expands and eventually covers most of the jet’s cross-section. The expansion is enhanced as more energy from the jet is converted into kinetic and internal energy of the ejecta, which also favours the ejecta disruption, all of this occurs on timescales of ∼10⁴ yr. Although a complete numerical convergence of the results is unattainable given the subsonic, turbulent nature of the interaction region, the simulations are consistent in their description of the gross morphological and dynamical properties of the interaction process.

Conclusions. At the end of the simulations, the supernova ejecta already partially mixed with the relativistic jet. The results also suggest that the jet-ejecta interaction may be a non-negligible non-thermal emitter. Moreover, due to efficient mixing, the interaction region can be a potential source of ultra-high-energy cosmic rays of heavy composition.