High-mass stars are thought to accumulate much of their mass via short, infrequent bursts of disk-aided accretion1,2. Such accretion events are rare and difficult to observe directly but are known to drive enhanced maser emission3,4,5,6. In this Letter we report high-resolution, multi-epoch methanol maser observations toward G358.93-0.03, which reveal an interesting phenomenon: the subluminal propagation of a thermal radiation ‘heatwave’ emanating from an accreting high-mass protostar. The extreme transformation of the maser emission implies a sudden intensification of thermal infrared radiation from within the inner (40-mas, 270-au) region. Subsequently, methanol masers trace the radial passage of thermal radiation through the environment at ≥4% of the speed of light. Such a high translocation rate contrasts with the ≤10 km s−1 physical gas motions of methanol masers typically observed using very-long-baseline interferometry (VLBI). The observed scenario can readily be attributed to an accretion event in the high-mass protostar G358.93-0.03-MM1. While being the third case in its class, G358.93-0.03-MM1 exhibits unique attributes hinting at a possible ‘zoo’ of accretion burst types. These results promote the advantages of maser observations in understanding high-mass-star formation, both through single-dish maser monitoring campaigns and via their international cooperation as VLBI arrays.
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The data that support the plots within this paper and other findings of this study are available from the PAWSEY data archive (https://data.pawsey.org.au/public/?path=/VLBI/Archive/LBA/vx026) or from the corresponding author on reasonable request
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R.A.B. acknowledges support through the EACOA Fellowship from the East Asian Core Observatories Association. S.P.E., G.O. and L.H. acknowledge the support of the ARC Discovery Project (project number DP180101061). G.O. was supported by CAS LCWR grant 2018-XBQNXZ-B-021. A.M.S. was supported by the Foundation for the Advancement of Theoretical Physics and Mathematics “BASIS”. This work was supported by JSPS KAKENHI grant JP19K03921. T.H. is financially supported by the MEXT/JSPS KAKENHI grants 16K05293 and 17K05398. J.O.C. acknowledges support by the Italian Ministry of Foreign Affairs and International Cooperation (MAECI Grant Number ZA18GR02) and the South African Department of Science and Technology’s National Research Foundation (DST-NRF Grant Number 113121) as part of the ISARP RADIOSKY2020 Joint Research Scheme. This work was supported by the National Science Centre, Poland, through grant 2016/21/B/ST9/01455. The LBA is part of the Australia Telescope National Facility, which is funded by the Australian Government for operation as a National Facility managed by CSIRO. This work was supported by resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
The authors declare no competing interests.
Peer review information Nature Astronomy thanks Sandra Etoka and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Burns, R.A., Sugiyama, K., Hirota, T. et al. A heatwave of accretion energy traced by masers in the G358-MM1 high-mass protostar. Nat Astron (2020). https://doi.org/10.1038/s41550-019-0989-3