skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Molecular Outflows: Explosive versus Protostellar

Abstract

With the recent recognition of a second, distinctive class of molecular outflows, namely the explosive ones not directly connected to the accretion–ejection process in star formation, a juxtaposition of the morphological and kinematic properties of both classes is warranted. By applying the same method used in Zapata et al., and using {sup 12}CO( J = 2-1) archival data from the Submillimeter Array, we contrast two well-known explosive objects, Orion KL and DR21, to HH 211 and DG Tau B, two flows representative of classical low-mass protostellar outflows. At the moment, there are only two well-established cases of explosive outflows, but with the full availability of ALMA we expect that more examples will be found in the near future. The main results are the largely different spatial distributions of the explosive flows, consisting of numerous narrow straight filament-like ejections with different orientations and in almost an isotropic configuration, the redshifted with respect to the blueshifted components of the flows (maximally separated in protostellar, largely overlapping in explosive outflows), the very-well-defined Hubble flow-like increase of velocity with distance from the origin in the explosive filaments versus the mostly non-organized CO velocity field in protostellar objects, and huge inequalities in mass, momentum, andmore » energy of the two classes, at least for the case of low-mass flows. Finally, all the molecular filaments in the explosive outflows point back to approximately a central position (i.e., the place where its “exciting source” was located), contrary to the bulk of the molecular material within the protostellar outflows.« less

Authors:
; ; ;  [1];  [2]
  1. Instituto de Radioastronomía y Astrofísica, UNAM, Apdo. Postal 3-72 (Xangari), 58089 Morelia, Michoacán, México (Mexico)
  2. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121, Bonn (Germany)
Publication Date:
OSTI Identifier:
22663795
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 836; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; AVAILABILITY; CARBON; CARBON MONOXIDE; CONFIGURATION; EXPLOSIVES; FILAMENTS; MASS; PROTOSTARS; RED SHIFT; SPATIAL DISTRIBUTION; STARS; VELOCITY

Citation Formats

Zapata, Luis A., Rodríguez, Luis F., Palau, Aina, Loinard, Laurent, and Schmid-Burgk, Johannes. Molecular Outflows: Explosive versus Protostellar. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA5B94.
Zapata, Luis A., Rodríguez, Luis F., Palau, Aina, Loinard, Laurent, & Schmid-Burgk, Johannes. Molecular Outflows: Explosive versus Protostellar. United States. doi:10.3847/1538-4357/AA5B94.
Zapata, Luis A., Rodríguez, Luis F., Palau, Aina, Loinard, Laurent, and Schmid-Burgk, Johannes. Fri . "Molecular Outflows: Explosive versus Protostellar". United States. doi:10.3847/1538-4357/AA5B94.
@article{osti_22663795,
title = {Molecular Outflows: Explosive versus Protostellar},
author = {Zapata, Luis A. and Rodríguez, Luis F. and Palau, Aina and Loinard, Laurent and Schmid-Burgk, Johannes},
abstractNote = {With the recent recognition of a second, distinctive class of molecular outflows, namely the explosive ones not directly connected to the accretion–ejection process in star formation, a juxtaposition of the morphological and kinematic properties of both classes is warranted. By applying the same method used in Zapata et al., and using {sup 12}CO( J = 2-1) archival data from the Submillimeter Array, we contrast two well-known explosive objects, Orion KL and DR21, to HH 211 and DG Tau B, two flows representative of classical low-mass protostellar outflows. At the moment, there are only two well-established cases of explosive outflows, but with the full availability of ALMA we expect that more examples will be found in the near future. The main results are the largely different spatial distributions of the explosive flows, consisting of numerous narrow straight filament-like ejections with different orientations and in almost an isotropic configuration, the redshifted with respect to the blueshifted components of the flows (maximally separated in protostellar, largely overlapping in explosive outflows), the very-well-defined Hubble flow-like increase of velocity with distance from the origin in the explosive filaments versus the mostly non-organized CO velocity field in protostellar objects, and huge inequalities in mass, momentum, and energy of the two classes, at least for the case of low-mass flows. Finally, all the molecular filaments in the explosive outflows point back to approximately a central position (i.e., the place where its “exciting source” was located), contrary to the bulk of the molecular material within the protostellar outflows.},
doi = {10.3847/1538-4357/AA5B94},
journal = {Astrophysical Journal},
number = 1,
volume = 836,
place = {United States},
year = {Fri Feb 10 00:00:00 EST 2017},
month = {Fri Feb 10 00:00:00 EST 2017}
}
  • We report the results of a series of AMR radiation-hydrodynamic simulations of the collapse of massive star forming clouds using the ORION code. These simulations are the first to include the feedback effects protostellar outflows, as well as protostellar radiative heating and radiation pressure exerted on the infalling, dusty gas. We find that that outflows evacuate polar cavities of reduced optical depth through the ambient core. These enhance the radiative flux in the poleward direction so that it is 1.7 to 15 times larger than that in the midplane. As a result the radiative heating and outward radiation force exertedmore » on the protostellar disk and infalling cloud gas in the equatorial direction are greatly diminished. The simultaneously reduces the Eddington radiation pressure barrier to high-mass star formation and increases the minimum threshold surface density for radiative heating to suppress fragmentation compared to models that do not include outflows. The strength of both these effects depends on the initial core surface density. Lower surface density cores have longer free-fall times and thus massive stars formed within them undergo more Kelvin contraction as the core collapses, leading to more powerful outflows. Furthermore, in lower surface density clouds the ratio of the time required for the outflow to break out of the core to the core free-fall time is smaller, so that these clouds are consequently influenced by outflows at earlier stages of collapse. As a result, outflow effects are strongest in low surface density cores and weakest in high surface density one. We also find that radiation focusing in the direction of outflow cavities is sufficient to prevent the formation of radiation pressure-supported circumstellar gas bubbles, in contrast to models which neglect protostellar outflow feedback.« less
  • VLA observations of Sgr B2 in six ammonia transitions have uncovered two 200-K condensations with approximately 0.2 pc diameters associated with water maser sources which are similar to the Orion hot core but are more massive. Total NH3 mass of the northern source is 1000 times higher than in the Orion hot core. The hot core emission traces dense gas around newly formed massive stars, and is produced during a relatively brief stage after the star begins to heat the surrounding medium and before the dense gas is dispersed by outflow and the emergence of an expanding H II region.more » 36 references.« less
  • We examine emission from a young protostellar object (YPO) with three-dimensional ideal magnetohydrodynamic (MHD) simulations and three-dimensional non-local thermodynamic equilibrium line transfer calculations, and show the first results. To calculate the emission field, we employed a snapshot result of an MHD simulation having young bipolar outflows and a dense protostellar disk (a young circumstellar disk) embedded in an infalling envelope. Synthesized line emission of two molecular species (CO and SiO) shows that subthermally excited SiO lines as a high-density tracer can provide a better probe of the complex velocity field of a YPO, compared to fully thermalized CO lines. Inmore » a YPO at the earliest stage when the outflows are still embedded in the collapsing envelope, infall, rotation, and outflow motions have similar speeds. We find that the combined velocity field of these components introduces a great complexity in the line emissions through varying optical thickness and emissivity, such as asymmetric double-horn profiles. We show that the rotation of the outflows, one of the features that characterizes an outflow driven by magneto-centrifugal forces, appears clearly in velocity channel maps and intensity-weighted mean velocity (first moment of velocity) maps. The somewhat irregular morphology of the line emission at this youngest stage is dissimilar to a more evolved object such as young Class 0. High angular resolution observation by, e.g., the Atacama Large Millimeter/submillimeter Array telescope can reveal these features. Our results demonstrate a powerful potential of the synthesized emission of the three-dimensional line transfer to probe the velocity field embedded in the envelope, and further analysis will be able to determine the precise velocity field to assess the dynamics in the YPO to gain a better understanding of star formation.« less
  • In star formation, magnetic fields act as a cosmic angular momentum extractor that increases mass accretion rates onto protostars and, in the process, creates spectacular outflows. However, recently it has been argued that this magnetic brake is so strong that early protostellar disks-the cradles of planet formation-cannot form. Our three-dimensional numerical simulations of the early stages of collapse (approx<10{sup 5} yr) of overdense star-forming clouds form early outflows and have magnetically regulated and rotationally dominated disks (inside 10 AU) with high accretion rates, despite the slip of the field through the mostly neutral gas. We find that in three dimensionsmore » magnetic fields suppress gravitationally driven instabilities that would otherwise prevent young, well-ordered disks from forming. Our simulations have surprising consequences for the early formation of disks, their density and temperature structure, the mechanism and structure of early outflows, the flash heating of dust grains through ambipolar diffusion, and the origin of planets and binary stars.« less
  • We report the results of spectroscopic mapping observations carried out toward protostellar outflows in the BHR71, L1157, L1448, NGC 2071, and VLA 1623 molecular regions using the Infrared Spectrograph (IRS) of the Spitzer Space Telescope. These observations, covering the 5.2-37 mum spectral region, provide detailed maps of the eight lowest pure rotational lines of molecular hydrogen and of the [S I] 25.25 mum and [Fe II] 26.0 mum fine-structure lines. The molecular hydrogen lines, believed to account for a large fraction of the radiative cooling from warm molecular gas that has been heated by a non-dissociative shock, allow the energeticsmore » of the outflows to be elucidated. Within the regions mapped toward these five outflow sources, total H{sub 2} luminosities ranging from 0.02 to 0.75 L{sub sun} were inferred for the sum of the eight lowest pure rotational transitions. By contrast, the much weaker [Fe II] 26.0 mum fine-structure transition traces faster, dissociative shocks; here, only a small fraction of the fast shock luminosity emerges as line radiation that can be detected with Spitzer/IRS.« less