X-ray emission from comets, cometary knots, and supernova remnants

A comparison is made between one of the processes leading to cometary X-ray emission and X-rays from supernova remnants. We demonstrate that the X-ray emission in both comet and supernova is bremsstrahlung and line radiation created by energetic electrons accelerated by plasma turbulence. We further demonstrate that the most likely source of plasma turbulence is produced by counterstreaming ion populations which result from the mass loading effect or from an anisotropic distribution produced by reflecting ions from a collisionless shock. The instability that gives rise to the plasma turbulence is the modified two-stream instability of counterstreaming ions. A similar instability arises in laser-plasma interactions that have self-generating magnetic fields and flowing ions.