MAGNETIC-FIELD DISSIPATION IN DENSE MOLECULAR CLOUDS

In dense molecular clouds the grains become the main charged particles . When the hydrogen gas density reaches as high as n(H) = 10(11) cm(-3 ) and the grains are assumed to be small polycyclic aromatic hydrocarb ons(PAHs), the lower hybrid drift instability develops, leading to the creation of anomalous electric conductivity, which makes the magnetic Reynold's number of the system R-M similar to 1 indicating the dissip ation of magnetic fields. When the gas density continues to go up and over 10(11) cm(-3), the collision frequency between PAHs and gas parti cles becomes larger than the plasma frequency, resulting in the collis ion process being dominant. In that case the magnetic field also dissi pates because R-M similar to 1 is still kept.