Dissipation of kinetic energy in clumpy magnetic clouds

Abstract

The dissipation of the kinetic energy of magnetically connected clumps in a molecular cloud is discussed. For low interclump densities, dissipation is by ion-neutral viscosity inside the clumps and in the interclump medium. Additional kinetic energy is lost by Alfven wave propagation to the external medium. The internal dissipation is found to be slow enough that molecular clouds can remain cold in the presence of supersonic clump motions. Most dissipation is by wave propagation. In the absence of wave energy input from internal or external sources, the time scale for significant energy loss from a young giant molecular cloud is approximately 2 free fall times, and in a dense molecular cloud core it is approximately 15 free fall times.