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Title: Unveiling the Role of the Magnetic Field at the Smallest Scales of Star Formation

Abstract

We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of polarized dust emission from the protostellar source Ser-emb 8 at a linear resolution of 140 au. Assuming models of dust-grain alignment hold, the observed polarization pattern gives a projected view of the magnetic field structure in this source. Contrary to expectations based on models of strongly magnetized star formation, the magnetic field in Ser-emb 8 does not exhibit an hourglass morphology. Combining the new ALMA data with previous observational studies, we can connect magnetic field structure from protostellar core (∼80,000 au) to disk (∼100 au) scales. We compare our observations with four magnetohydrodynamic gravo-turbulence simulations made with the AREPO code that have initial conditions ranging from super-Alfvénic (weakly magnetized) to sub-Alfvénic (strongly magnetized). These simulations achieve the spatial dynamic range necessary to resolve the collapse of protostars from the parsec scale of star-forming clouds down to the ∼100 au scale probed by ALMA. Only in the very strongly magnetized simulation do we see both the preservation of the field direction from cloud to disk scales and an hourglass-shaped field at <1000 au scales. We conduct an analysis of the relative orientation of the magnetic field and the density structure in bothmore » the Ser-emb 8 ALMA observations and the synthetic observations of the four AREPO simulations. We conclude that the Ser-emb 8 data are most similar to the weakly magnetized simulations, which exhibit random alignment, in contrast to the strongly magnetized simulation, where the magnetic field plays a role in shaping the density structure in the source. In the weak-field case, it is turbulence—not the magnetic field—that shapes the material that forms the protostar, highlighting the dominant role that turbulence can play across many orders of magnitude in spatial scale.« less

Authors:
; ; ; ;  [1];  [2];  [3];  [4];  [5];  [6]
  1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  2. Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB, Carrer de Can Magrans S/N, E-08193 Cerdanyola del Vallès, Catalonia (Spain)
  3. National Radio Astronomy Observatory, Charlottesville, VA 22903 (United States)
  4. Heidelberger Institut für Theoretische Studien, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg (Germany)
  5. Department of Astronomy, University of Virginia, Charlottesville, VA 22903 (United States)
  6. Institute of Astronomy and Department of Physics, National Tsing Hua University, 101 Section 2 Kuang Fu Road, 30013 Hsinchu, Taiwan (China)
Publication Date:
OSTI Identifier:
22654457
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 842; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALFVEN WAVES; CLOUDS; COMPARATIVE EVALUATIONS; DENSITY; DUSTS; EMISSION; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; POLARIZATION; PRESERVATION; PROTOSTARS; RANDOMNESS; RESOLUTION; SIMULATION; STARS; TURBULENCE

Citation Formats

Hull, Charles L. H., Mocz, Philip, Burkhart, Blakesley, Goodman, Alyssa A., Hernquist, Lars, Girart, Josep M., Cortés, Paulo C., Springel, Volker, Li, Zhi-Yun, and Lai, Shih-Ping, E-mail: chat.hull@cfa.harvard.edu. Unveiling the Role of the Magnetic Field at the Smallest Scales of Star Formation. United States: N. p., 2017. Web. doi:10.3847/2041-8213/AA71B7.
Hull, Charles L. H., Mocz, Philip, Burkhart, Blakesley, Goodman, Alyssa A., Hernquist, Lars, Girart, Josep M., Cortés, Paulo C., Springel, Volker, Li, Zhi-Yun, & Lai, Shih-Ping, E-mail: chat.hull@cfa.harvard.edu. Unveiling the Role of the Magnetic Field at the Smallest Scales of Star Formation. United States. doi:10.3847/2041-8213/AA71B7.
Hull, Charles L. H., Mocz, Philip, Burkhart, Blakesley, Goodman, Alyssa A., Hernquist, Lars, Girart, Josep M., Cortés, Paulo C., Springel, Volker, Li, Zhi-Yun, and Lai, Shih-Ping, E-mail: chat.hull@cfa.harvard.edu. Tue . "Unveiling the Role of the Magnetic Field at the Smallest Scales of Star Formation". United States. doi:10.3847/2041-8213/AA71B7.
@article{osti_22654457,
title = {Unveiling the Role of the Magnetic Field at the Smallest Scales of Star Formation},
author = {Hull, Charles L. H. and Mocz, Philip and Burkhart, Blakesley and Goodman, Alyssa A. and Hernquist, Lars and Girart, Josep M. and Cortés, Paulo C. and Springel, Volker and Li, Zhi-Yun and Lai, Shih-Ping, E-mail: chat.hull@cfa.harvard.edu},
abstractNote = {We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of polarized dust emission from the protostellar source Ser-emb 8 at a linear resolution of 140 au. Assuming models of dust-grain alignment hold, the observed polarization pattern gives a projected view of the magnetic field structure in this source. Contrary to expectations based on models of strongly magnetized star formation, the magnetic field in Ser-emb 8 does not exhibit an hourglass morphology. Combining the new ALMA data with previous observational studies, we can connect magnetic field structure from protostellar core (∼80,000 au) to disk (∼100 au) scales. We compare our observations with four magnetohydrodynamic gravo-turbulence simulations made with the AREPO code that have initial conditions ranging from super-Alfvénic (weakly magnetized) to sub-Alfvénic (strongly magnetized). These simulations achieve the spatial dynamic range necessary to resolve the collapse of protostars from the parsec scale of star-forming clouds down to the ∼100 au scale probed by ALMA. Only in the very strongly magnetized simulation do we see both the preservation of the field direction from cloud to disk scales and an hourglass-shaped field at <1000 au scales. We conduct an analysis of the relative orientation of the magnetic field and the density structure in both the Ser-emb 8 ALMA observations and the synthetic observations of the four AREPO simulations. We conclude that the Ser-emb 8 data are most similar to the weakly magnetized simulations, which exhibit random alignment, in contrast to the strongly magnetized simulation, where the magnetic field plays a role in shaping the density structure in the source. In the weak-field case, it is turbulence—not the magnetic field—that shapes the material that forms the protostar, highlighting the dominant role that turbulence can play across many orders of magnitude in spatial scale.},
doi = {10.3847/2041-8213/AA71B7},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 842,
place = {United States},
year = {Tue Jun 20 00:00:00 EDT 2017},
month = {Tue Jun 20 00:00:00 EDT 2017}
}