Detection of Irregular, Sub-mm Opaque Structures in the Orion Molecular
  Clouds: Protostars within 10000 years of formation?
  We report ALMA and VLA continuum observations that potentially identify the
four youngest protostars in the Orion Molecular Clouds taken as part of the
Orion VANDAM program. These are distinguished by bright, extended, irregular
emission at 0.87 mm and 8 mm and are optically thick at 0.87 mm. These
structures are distinct from the disk or point-like morphologies seen toward
the other Orion protostars. The 0.87 mm emission implies temperatures of 41-170
K, requiring internal heating. The bright 8 mm emission implies masses of 0.5
to 1.2 M_sun assuming standard dust opacity models. One source has a Class 0
companion, while another exhibits substructure indicating a
companion-candidate. Three compact outflows are detected, two of which may be
driven by companions, with dynamical times of ~300 to ~400 years. The slowest
outflow may be driven by a first hydrostatic core. These protostars appear to
trace an early phase when the centers of collapsing fragments become optically
thick to their own radiation and compression raises the gas temperature. This
phase is thought to accompany the formation of hydrostatic cores. A key
question is whether these structures are evolving on free fall times of ~100
years, or whether they are evolving on Kelvin-Helmholtz times of several
thousand years. The number of these sources imply a lifetime of ~6000 years, in
closer agreement with the Kelvin-Helmholtz time. In this case, rotational
and/or magnetic support could be slowing the collapse.
