CfA Colloquium: November 14, 2002

Speaker: Eve Ostriker (U. Maryland)

Title: Creative Tension: Galactic Magnetic Fields and the Origins of Star-Forming Clouds

Abstract: In the Milky Way and other contemporary spiral galaxies, most star formation takes place within giant molecular clouds (GMCs). Both observations and theory argue that these clouds form and disperse rapidly, but the dynamical mechanisms involved are only incompletely understood. Magnetic tension and a variety of other physical effects may contribute in helping and hindering the creation of GMCs; I will explain how these processes interact in several candidate instability mechanisms. I will then present results from new numerical simulations that identify the most promising candidates from among the contenders, in particular favoring self-gravitating instabilities over the more traditional Parker mechanism. These new models also explain the formation of fascinating spur-like dust lanes recently observed in high-resolution HST images of spiral galaxies. Finally, I will discuss how the interplay of magnetic tension, rotation, and shear may induce quite different ISM dynamics in spiral arm versus interarm regions, and how these differences may be important in a quantitative understanding of the masses of GMCs.