Evidence for magnetic and virial equilibrium in molecular clouds

Abstract

Recent measurements of the magnetic-field strength, velocity dispersion, and size of 14 molecular clouds agree, within uncertainty of a factor of about 2, with the predictions of a simple model in which the magnetic, kinetic, and gravitational energies are all equal. The clouds range from extended dark clouds to massive dense cores associated with OH masers and compact H II regions. Their field strengths range over a factor of about 1000, from about 10 microG to about 10 mG. This result suggests that the magnetic contribution to the internal motions and energy of many molecular clouds is crucial for cloud dynamics, cloud evolution, and star formation.