Charles J. Lada

Rossi Lectures: The Modern Problem of Galactic Star Formation. Initial conditions: IR extinction and the structure of dense cloud cores, the nature of protostars and the origin of the IMF

Stars and Planetary Systems are formed in the visibly dark and dense cores of molecular clouds which are the coldest objects in the universe. Despite more than three decades of study using millimeter-wave and infrared techniques, suprisingly little is known or understood about the detailed structure and evolution these objects. Yet, the physical conditions in such dense cores, particularly those that have yet to form stars and planets, describe the initial conditions for star formation. Knowledge of such conditions is necessary for the successful development of any theory of stellar and planetary origins. In this talk I will discuss how deep infrared observations of background stars observed through dark cloud cores are now revealing new information, in unprecedented detail, about the structure, physical state and evolution of these dense, cold objects. I will report the recent determination of the mass function for a complete sample of dense cores within a single molecular cloud. Based on these observations I will argue that the origin of the stellar IMF is the direct result of the simple product of the dense core mass function and a uniform star formation efficiency of about 30%. I will discuss evidence that suggests that the dense core mass function itself may originate in a process of simple thermal (Jeans) fragmentation. I will also present new observations taken with the Spitzer Space Telescope which may provide some support for this latter idea. I will also offer some speculations concerning the origin of stellar multiplicity and its observed mass dependence. Finally, time permitting, I will discuss the recent extension of such extinction work to nearby spiral galaxies.

Ritorna alla Pagina dei Seminari