International Journal of Physics | Vol. 17, No. 8, August 2026 | pp. 81–88
DOI: 10.46882/2026/IJP/000199
Research Article
Title: Relativistic Jet Deceleration and Magnetohydrodynamic Instabilities in Inhomogeneous Interstellar Medium
Names of Authors: G. V. Bruno¹, C. M. Martinez², L. A. O’Connor³
Authors’ Affiliations:
¹ Department of Astrophysics, University of Bologna, Bologna, Italy
² Instituto de Astrofísica de Andalucía, CSIC, Granada, Spain
³ School of Cosmic Physics, Dublin Institute for Advanced Studies, Dublin, Ireland
Abstract: The deceleration of relativistic jets in gamma-ray bursts (GRBs) and active galactic nuclei (AGN) depends heavily on the density profile of the surrounding ambient medium. We performed high-resolution two-dimensional relativistic hydrodynamic simulations to model jet propagation into an inhomogeneous interstellar medium. The ambient medium was configured with periodic density fluctuations ranging over two orders of magnitude (from 0.01 to 1.00 particles/cm³). The initial jet Lorentz factor was set to W = 50, and the jet-to-ambient matter density ratio was 0.001. Our numerical results show that when the relativistic jet impacts high-density clouds, it triggers strong reverse shocks that propagate backward into the jet core. These reverse shocks cause significant kinetic energy dissipation, reducing the bulk Lorentz factor by up to 35.0% within a propagation distance of 1.0 pc. The interaction creates high-pressure regions and severe Kelvin-Helmholtz instabilities along the jet boundary. These instabilities lead to strong turbulent mixing and the formation of a prominent forward shock cocoon. We extracted synthetic synchrotron emission profiles from the simulated pressure and magnetic field distributions. The light curves exhibit distinct, short-term flux variability and temporal variability indices fluctuating between -1.1 and -1.5 during the deceleration phase. These simulated emission spikes match the early-time X-ray and optical afterglow flares observed in several astrophysical events. Consequently, these findings offer a coherent structural explanation for the erratic light curves recorded by modern space telescopes.
Keywords: Relativistic hydrodynamics; Gamma-ray bursts; Active galactic nuclei; Interstellar medium; Shock waves; Synchrotron emission
Manuscript Timeline: Received: April 22, 2026 / Revised: June 01, 2026 / Accepted: June 22, 2026 / Published: August 14, 2026
Citation: Bruno, G. V., Martinez, C. M., & O’Connor, L. A. (2026). Relativistic Jet Deceleration and Magnetohydrodynamic Instabilities in Inhomogeneous Interstellar Medium. International Journal of Physics, 17(8), 81–88.
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