Patricio Sanhueza and colleagues reported on ALMA high resolution observations of the high-mass star forming region IRAS 18089-1732. They revealed that, the dense molecular envelope surrounding the high-mass star has a complex spiral pattern at the 0.003–0.1 pc scales. Their study recently appeared in Arxiv.
In order to fully understand high-mass star formation, we have to study the magnetic fields. But, it is by far the least explored. Polarization observations can help us to infer the magnetic field in molecular clouds and denser regions associated with star formation. But, at smaller scales i.e. at core-disk interface ~ 1000 au, these observations are far less. Thus, it is difficult to evaluate the importance of the magnetic field in the high mass star formation process.
IRAS 18089−1732, is the high-mass star forming region, located at a parallax distance of 2.34 kpc with a bolometric luminosity of 1.3 × 10⁴ L. It is an ideal laboratory to assess the importance of the magnetic field with respect to turbulence, gravity, and rotation. Earlier studies at arcsec resolution showed that IRAS 18089−1732 has a deeply embedded hot core and a disklike rotating structure roughly perpendicular to a molecular outflow.
Now, Patricio Sanhueza and colleagues reported ALMA 1.2 mm, high-resolution (700 au) dust polarization and molecular line observations of the rotating hot molecular core embedded in the high-mass star-forming region IRAS 18089−1732.
They revealed that the dense molecular envelope surrounding the high-mass star has a complex spiral pattern (much like whirlpool) at the 0.003–0.1 pc scales. This spiral-like morphology is seen in the gas and dust, as well as in the magnetic field.
They have also modeled the magnetic field and found that, the core is weakly magnetized. The estimated magnetic field strength and Alfven speed are 3.5 mG and 1.26 km s¯1, respectively.
In addition, they analyzed the energy balance of the system and showed that, the high-mass star formation can occur in weakly magnetized environments and that gravity is shaping the immediate surrounding (~1000 au scales) around the high-mass star. While, the magnetic field importance is only comparable to turbulence and rotation.
“The overwhelming importance of gravity with respect to the other energies becomes more evident once we included the magnetic field and rotation and calculated the virial parameters.”
Moreover, the spiral magnetic field indicated that, angular momentum is high enough to twist the field lines, as supported by the model and the energy analysis.
“With these observations, we suggest that the importance of the magnetic field in the process of high-mass star formation depends on the size scales traced and the evolutionary stage of the observed region.”— concluded authors of the study
Featured image: ALMA 1.2 mm dust continuum emission (color scale and contours) toward IRAS 18089-1732 with overlaid magnetic field vectors, which correspond to the dust polarization vectors rotated by 90 deg. Yellow line segments representing the magnetic field orientation are plotted above the 3σ level, with σ = 31.4 µJy beam¯1, and have an arbitrary length. Contours correspond to the dust continuum emission in steps of 4, 6, 10, 18, 34, 66, 130, 258, 514 times the σ (rms) value of 175 µJy beam¯1. Spatial resolution of 700 au (0.3″) is shown on the bottom left. Scale bar is shown on the bottom, right side of the panel. © Patricio Sanhueza et al.
Reference: Patricio Sanhueza, Josep Miquel Girart, Marco Padovani, Daniele Galli, Charles L. H. Hull, Qizhou Zhang, Paulo Cortes, Ian W. Stephens, Manuel Fernandez-Lopez, James M. Jackson, Pau Frau, Patrick M. Kock, Benjamin Wu, Luis A. Zapata, Fernando Olguin, Xing Lu, Andrea Silva, Ya-Wen Tang, Takeshi Sakai, Andres E. Guzman, Ken’ichi Tatematsu, Fumitaka Nakamura, Huei-Ru Vivien Chen, “Gravity Driven Magnetic Field at ~1000 au Scales in High-mass Star Formation”, Arxiv, 2021. https://arxiv.org/abs/2106.03866
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