The Youngest Protostars in the Orion Molecular Cloud: Observations Revealing the Physics of Protostar Formation*

We present a study five of the most deeply embedded protostars (stars still accreting mass) known in the Orion Molecular Clouds, identified with the Herschel Space Observatory by their bright emission at 70 microns as part of the Herschel Orion Protostar Survey. Using the Atacama Large Millimeter Array (ALMA) and Very Large Array (VLA) radio interferometers, we map the thermal dust emission at 0.87 mm and 8 mm.  Using the Planck function, we analyze this emission, which arises from the ~50 K dust grains in the collapsing gas clouds forming the stars.  We show images of dense structures in the inner regions of the collapsing gas clouds, and argue that these are images are within 10,000 years of onset of star formation that has previously been limited to theoretical work.

Resolving structures down to 40 AU with high optical depth shows  that radiation cooling is inefficient in these regions. We estimate dust masses of up to ~1.5 solar masses concentrated  in regions 160 AU in extent from the 8 mm data. These data gives us the first observational insights into the adiabatic contraction phases of the gas clouds that initiates the formation of hydrostatically supported protostars (see Larson 1969 and Bhandare et al. 2018).