Understanding the physics of the various instabilities and finding their timescales is an important problem in Laboratory and Astrophysical plasmas. Using numerical simulations but mostly analytical work in the linear regime we study their onset in various settings: (i) in the X and Z-pinch experiments in the Centre for Plasma Physics & Lasers, (ii) in AGN and GRB relativistic magnetized jets, (iii) in magnetized accretion disks around Kerr black holes.
The formation of jets in a variety of Astrophysical settings is often attributed to the action of magnetic fields, that efficiently tap the rotational energy of the source and accelerate plasma to high bulk velocities. We have examined the problem in both non-relativistic and relativistic flows in the framework of Special Relativity, and we continue the study in the context of General Relativity, trying to understand how the spacetime around a rotating black hole affects the bulk acceleration and collimation of jets.
Polarization observations are perhaps the only way to understand the magnetic field topology in relativistic AGN jets. Using the magnetic field and density distributions from magnetohydrodynamic jet models we can find the corresponding maps for all the Stokes parameters and compare them with the observations.
Very often in Astrophysics we have high-velocity fluid collisions, which we treat as Riemann problems (combinations of shock waves, rarefaction waves and contact discontinuities). We have studied and continue to work on their implementation on (i) Cepheid wind structure and its relation to recently observed phase-dependent X-ray emission, (ii) interaction of an AGN jet with its environment, (iii) role of rarefaction acceleration when a GRB jet crosses the surface of the progenitor star.
Department of Physics National and Kapodistrian University of Athens University Campus GR-157 84 Zografou, Athens