Relativistic hydrodynamics simulations of supernova explosions within extragalactic jets

TL;DR

This study uses relativistic hydrodynamics simulations to investigate the interaction of supernova ejecta with extragalactic jets, focusing on two geometries (2D axisymmetric and 3D with stellar orbital motion) and two ejecta sizes. The ejecta rapidly expands to cover a large fraction of the jet cross-section, transferring jet energy into kinetic and internal energy of the ejecta and triggering strong instabilities that disrupt and mix the ejecta with the jet on timescales of about $10^4$ years. The simulations show substantial jet mass-loading, transient jet deceleration, and efficient mixing that can seed non-thermal emission and potentially accelerate heavy nuclei to ultra-high energies, with implications for observed AGN jet energetics and high-energy phenomena. The work highlights the role of dimensionality, resolution, and orbital motion in shaping the evolution, and points to magnetic-field effects and a broader parameter space as directions for future magnetohydrodynamic studies and observational predictions.

Abstract

Jets in active galactic nuclei have to cross significant distances within their host galaxies, meeting large numbers of stars of different masses and evolution stages in their paths. Given enough time, supernova explosions within the jet will eventually happen, and may have a strong impact on its dynamics, potentially triggering powerful non-thermal activity. We carried out a detailed numerical study to explore the dynamics of the interaction between the ejecta of a supernova explosion and a relativistic extragalactic jet. 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. Although initially filling a region much smaller than the jet radius, the ejecta expands and eventually covers most of the jet cross section. The expansion is enhanced as more energy from the jet is converted into kinetic and internal energy of the ejecta, which also favors the ejecta disruption, all this occurring on timescales ~ 10^4 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. At the end of the simulations, the supernova ejecta has 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.

Figures (15)

• Figure 1: Snapshot of a jet-SN interaction during the initial phase to illustrate the set-up of the 2D axisymmetric simulations. Upper half: rest-mass density, $\rho$. Lower half: axial velocity, $v_z$. The white dashed-line gives the jet-mass fraction contour for the tracer value $f=0.5$. The jet flow is filling the grid but in the ejecta region, and propagates from left to right.
• Figure 2: Time evolution of the rest-mass density (upper half panels) and axial velocity (lower half panels, mirror of the upper panels) for S1 in 2D. The black lines give the contour of the jet-mass fraction for the tracer value $f=0.5$. The jet is propagating from the left to the right. Top left: $t\approx 1600$ yr from the start of the simulation; top right: $t\approx2300$ yr; bottom left: $t\approx3000$ yr; bottom right: $t\approx 3800$ yr.
• Figure 3: Time evolution of the rest-mass density for S1 in 3D, with six 2D cuts in the $XY$-plane at $z=0$. The jet is propagating from the left to the right. Top left: $t\approx180$ yr; top middle: $t\approx1600$ yr; top right: $t\approx2300$ yr; bottom left: $t\approx3000$ yr; bottom middle: $t\approx3800$ yr; bottom right: $t\approx 4700$ yr.
• Figure 4: Time evolution of the temperature (upper half panels) and the tracer of jet mass-fraction (lower half panels) for S1 in 3D, with 6 2D cuts in the $XY$-plane and at $z=0$; the lower half corresponds to the same region shown in the upper half, but inverted with respect to the axis on $x=0$. The jet is propagating from the left to the right. Top left: $t\approx 180$ yr; top middle: $t\approx1600$ yr; top right: $t\approx2300$ yr; bottom left: $t\approx3000$ yr; bottom middle: $t\approx 3800$ yr; bottom right: $t\approx 4700$ yr.
• Figure 5: Colored surfaces of the rest-mass density 3D distribution, in code units, for the evolved structure of simulation S1 at $t\approx3000$ yr, corresponding to the bottom left panel of Fig. \ref{['3d_timeframe_rho_hr']}. The axis of the jet is in the middle of the $XZ$-plane, and the latter propagates along the $Y$-axis (triad visible on the bottom left of the image) and from the left to the right; the surfaces show the shocked ejecta interacting with the jet flow, while the nearly transparent red layer surrounding the shocked ejecta outlines the shocked jet region.