Two Massive, Low-Luminosity Cores Toward Infrared Dark Clouds
  This article presents high-resolution interferometric mosaics in the 850
micron waveband of two massive, quiescent infrared dark clouds. The two clouds
were chosen based on their likelihood to represent environments preceding the
formation of massive stars. The brightest compact sources detected in each
cloud have masses of approximately 110 and 60 solar masses with radii < 0.1 pc,
implying mean volume densities of approximately 1 million particles per cubic
centimeter and mean column densities of about 1 gram per square centimeter.
Supplementary data show these cores to be cold and inactive. Low upper limits
to their bolometric luminosities and temperatures place them at a very early
stage of evolution while current models of massive star formation suggest they
have the potential to form massive stars.
