Detection of Irregular, Submillimeter Opaque Structures in the Orion Molecular Clouds: Protostars within 10,000 yr of Formation?

We report Atacama Large Millimeter/submillimeter Array and Very Large Array 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 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 0.5-1.2 M o˙ 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 ∼1400 yr. 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 freefall times of ∼100 yr, or whether they are evolving on Kelvin-Helmholtz times of several thousand years. The number of these sources imply a lifetime of ∼6000 yr, in closer agreement with the Kelvin-Helmholtz time. In this case, rotational and/or magnetic support could be slowing the collapse. © 2020. The American Astronomical Society. All rights reserved.We wish to thank the anonymous referee for insightful comments and suggestions that improved the quality of this manuscript. The authors acknowledge Lee Hartmann for the useful discussions and many insightful comments. Support for Nicole Karnath was provided by the NSF through award SOSP AST-1519126 from the NRAO and by the NASA Origin of the Solar System program 13-OSS13-0094 (Megeath PI for both). This work made use of the SIMBAD database, the Vizier database, and the NASA Astrophysics Data System, funded by the National Aeronautics and Space Administration and the NSF. A.S. acknowledges funding through Fondecyt regular (project code 1180350), "Concurso Proyectos Internacionales de Investigacion" (project code PII20150171), and Chilean Centro de Excelencia en Astrofisica y Tecnologias Afines (CATA) BASAL grant AFB-170002. J.J.T. acknowledges funding from the National Science Foundation AST-1814762. Z.Y.L. is supported in part by NSF 1716259 and NASA 80NSSC18K1095. G.A., M.O., and A.K.D.-R. acknowledge financial support from the State Agency for Research of the Spanish MCIU through the AYA2017-84390-C2-1-R grant (co-funded by FEDER) and through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (SEV2017-0709). This research was conducted in part at the SOFIA Science Center, which is operated by the Universities Space Research Association under contract NNA17BF53C with the National Aeronautics and Space Administration. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2015.1.00041.S. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ.Peer reviewe