On the suppression of thermal conduction by magnetic fields

It is commonly assumed that ‘tangled’ magnetic fields can sufficiently suppress thermal transport to allow one to ignore thermal conduction in various astrophysical systems. In order to assess the validity of this assumption, we study the physics of thermal conduction in the presence of magnetic fields. Following previous work, we relate the effective suppression of thermal conductivity to the average length of magnetic field lines, and use geometric arguments to constrain the length of field lines by a normalized rms magnetic field strength. Numerical simulations are then used to examine the effects of fluid turbulence on field line stretching. Finally, as an illustration, our results are applied to cooling flow models, demonstrating that the magnetic suppression of thermal conductivity is not sufficiently effective in typical cluster haloes.