Interferometric observations of pre-main sequence disks - Caltech ...

CHAPTER 1
1.1 Star formation
Scientific overview
Star formation in our galaxy is a continuous process that occurs inside large concentra-
tions of cold gas and dust which contain more than 50% of the interstellar matter. Char-
acterized by temperatures of about 10 K, extents of tens of parsec and masses between
10 4 and 10 6 M⊙, the Giant Molecular Clouds are sustained against the gravitational
collapse by supersonic turbulent motions (Zuckerman and Evans, 1974) which lead to
strong density inhomogeneity inside the cloud. When the gravity on these smaller scale
condensations wins the gas pressure, the material collapses and the stellar formation
starts. During the contraction, clouds break in smaller parts following a fragmentation
process that ends with the formation of cores when the collapse becomes adiabatic, i.e.,
the gas compression corresponds to an increase in temperature. Before that, the col-
lapse has been isothermal since the gas density was too low to prevent the cooling of the
cloud.
Cores generally have extent of about 0.1 pc; the gas density is between 10 4 and
10 5 molecules cm −3 and the temperature is similar to the temperature of the original
molecular cloud. Given these properties, the typical core mass is of few M⊙, higher than