Pier Luca Rossi

Kelvin–Helmholtz instabilities in radiating flows

The linear Kelvin–Helmholtz stability regime of two radiating fluids in relative motion is discussed. The study is carried out in plane geometry and in the vortex‐sheet approximation. Attention is focused on the effects of radiation losses on the instability pattern: it is found that the principal effect is the suppression of the cutoff at Mach number M=2√2, typical of the adiabatic Kelvin–Helmholtz mode; in particular radiation effects are small on the instability below the cutoff, while they become dominant above. Radiating fluids are also typically affected by thermal instability. In fact thermal modes are found also in the present case: they may have growth rates comparable to the Kelvin–Helmholtz instability above the cutoff.

Nonlinear Evolution of Radiative Unstable Modes in Extragalactic Jets

Recent high resolution optical and radio observations of extragalactic sources show strong filamentary inhomogeneities of the emitting plasma, in their jets and lobes. Following the hypothesis that such structures could be formed by thermal instabilities driven by synchrotron radiation in a relativistic plasma (Simon and Axford, 1967), we study the nonlinear behaviour of such instabilities solving in a consistent way the equation of evolution of the distribution function of the emitting particles.