A Spontaneous Generation of the Magnetic Field and Suppression of the Heat Conduction in Cold Fronts

We have determined the physical mechanism responsible for the plasma instabilities, which was first found by Ramani and Laval (1978), associated with anisotropic velocity distributions induced by the temperature gradient in which there are growing low frequency transverse magnetic waves, even in the absence of background magnetic fields. We have shown that the physical mechanism responsible for the growth of one of the modes is identical to the Weibel instability. The nonlinear saturation level of the instability is also provided by considering the wave-particle interactions. The non-linear evolutions of the magnetic fields after the saturation are speculated. The results are applied to the cold fronts which is one of the newly discovered structures in clusters of galaxies by the Chandra X-ray observatory. We predict the existence of the magnetic field of ∼ 10μG tangential to the surface over the entire region of the cold front surface and that the heat conduction is significantly suppressed by the trapping of the electrons by the generated magnetic fields. The instability may provide a new possibility on the origin of cosmic magnetic field. Subject headings: galaxies: clusters: general—magnetic fields—conduction— instabilities—plasmas