Numerical simulations have predicted that substructures such as spiral arms can be produced through a gravitationally unstable disk around high-mass young stellar objects (HMYSOs)1,2,3,4,5. Recent high-resolution observations from the Atacama Large Millimeter/submillimeter Array have investigated these substructures at a spatial resolution of ~100 au (refs. 6,7,8,9,10). An accretion burst, which is a manifestation of an increase in the accretion rate caused by a gravitational instability in the disk1,11,12, can result in luminosity outbursting phenomena—as has been seen in several HMYSOs13,14. However, no clear relationship between the accretion bursts and disk substructures has been established. Here we report the detections of three new molecular maser species, HDO, HNCO and 13CH3OH, from the direction of the HMYSO G358.93-0.03 during a 6.7 GHz methanol maser flaring event15. High-quality imaging of the three new maser species exhibits consistent observational evidence that these masers closely trace the spiral-arm substructures around this HMYSO. The rapid decay of the spectral lines emitted from these molecules suggests that these are transient phenomena (for only ~1 month), probably associated with rapid changes in radiation field due to an accretion burst. Therefore, these new maser species provide evidence linking the spiral-arm substructure with an accretion burst, both expected from massive disk instabilities.
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The data from both TMRT and VLA that support the plots within this paper and other findings of this study are available from X.C. on reasonable request. Source data are provided with this paper.
The code for the pumping model of HDO and HNCO masers is available at https://github.com/ParfenovS/LVG_LRT
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We thank TMRT and VLA staff for their assistance in obtaining the data presented in this paper. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under agreement by the Associated Universities, Inc. X.C. was supported by the National Natural Science Foundation of China (grant numbers 11590781, 11873002, 12011530065 and 11590780), Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme (2019), Astronomy Science and Technology Research Laboratory of Department of Education of Guangdong Province, and Key Laboratory for Astronomical Observation and Technology of Guangzhou. A.M.S. and S.P. were supported by the Russian Science Foundation (grant number 18-12-00193). S.P.E. acknowledges the support of an ARC Discovery Project (project number DP180101061).
The authors declare no competing interests.
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Chen, X., Sobolev, A.M., Ren, Z. et al. New maser species tracing spiral-arm accretion flows in a high-mass young stellar object. Nat Astron (2020). https://doi.org/10.1038/s41550-020-1144-x