Quantifying the Kelvin-Helmholtz instability in interstellar jets with radiation observable on Earth

We present a new diagnostic method to both identify the presence of the Kelvin-Helmholtz instability (KHI) in interstellar plasma jets and determine its growth rate by measuring the emitted radiation.

Based on the electron dynamics inside the KHI vortices, we derive the emitted radiation power and polarization and show their correlation to the magnetic field evolution, driving the instability. These correlations are verified against simulations of the relativistic KHI using the 3D3V particle-in-cell code PIConGPU. It determines the angularly resolved radiation spectra for billions of electrons using generally valid Liénard-Wiechert potentials. The simulation shows that the growth rate correlation between radiation power and magnetic field agrees over orders of magnitude for the entire linear phase of the KHI while the polarization signature allows a clear identification of this phase.

The method presented can resolve the question whether the KHI occurs in astro-physical particle jets and furthermore provides quantitative insides to the jet dynamics by analyzing the radiation observable on Earth.