Star-Forming Motions in the Nearest Molecular Cloud Complexes

Philip C. Myers
Harvard-Smithsonian Center for Astrophysics


We describe recent observations of the nearest star-forming
complexes,  and their implications for star formation.  Molecular clouds
are highly nonuniform and turbulent, with  clumpy and filamentary
structure.  Some 1 % of a molecular cloud has density > 10^4 cm^(-3), and
these "dense cores" are well-established as formation sites of stars. How
such cores form stars is less clear.  New observations of starless cores
indicate that inward motions extend over ~0.2 pc, well beyond that expected
from the standard model of isolated star formation, "inside-out" collapse.
The typical speed of these motions is ~ 0.1 km/s, much faster than
expected from the standard model of dense core formation, subcritical
ambipolar diffusion. These motions may be explained by models which form
cores by dissipation of turbulence. New observations of cores with embedded
protostars also show extended inward motions, but in a few cases the
observed infall speed increases toward the protostar, suggesting a
transition from the slow motions of core formation to the fast motions of
star formation. Studying this transition will be an important focus of
high-resolution spectroscopy at millimeter and submillimeter wavelengths.