Magnetic field generation by the Weibel instability at temperature gradients in collisionless plasmas

The Weibel instability could be responsible for the generation of magnetic fields in various objects such as gamma-ray bursts, jets from active galactic nuclei, and clusters of galaxies. Using numerical simulations, the development of the Weibel instability at a temperature gradient is studied. It is found that current sheets are first generated at the gradient, and then they are rounded off and turn into current filaments. During this process, return currents are generated around the filaments and they prevent filaments from the merger. The magnetic fields around the filaments persist at least until t∼8000∕ωp, where ωp is the plasma frequency, and it is very likely that they survive for a much longer time.