A heatwave of accretion energy traced by masers in the G358-MM1 high-mass protostar

• Published in: Nature astronomy Vol. 4; no. 5; pp. 506 - 510
• Main Authors: Burns, R. A., Sugiyama, K., Hirota, T., Kim, Kee-Tae, Sobolev, A. M., Stecklum, B., MacLeod, G. C., Yonekura, Y., Olech, M., Orosz, G., Ellingsen, S. P., Hyland, L., Caratti o Garatti, A., Brogan, C., Hunter, T. R., Phillips, C., van den Heever, S. P., Eislöffel, J., Linz, H., Surcis, G., Chibueze, J. O., Baan, W., Kramer, B.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.05.2020; Nature Publishing Group
• Subjects: 639/33/34; 639/766/34/4126; 639/766/34/865; Accretion; Astronomy; Astrophysics and Cosmology; Emissions; Heat waves; Infrared radiation; Interferometry; International cooperation; Letter; Methanol; Physics; Physics and Astronomy; Star & galaxy formation; Thermal radiation; Translocation
• ISSN: 2397-3366; 2397-3366
• DOI: 10.1038/s41550-019-0989-3

High-mass stars are thought to accumulate much of their mass via short, infrequent bursts of disk-aided accretion 1 , 2 . Such accretion events are rare and difficult to observe directly but are known to drive enhanced maser emission 3 – 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. A ring of maser emission seemingly expanding at 0.05  c is actually tracing the propagation of heat through the circumstellar medium around a high-mass protostar rather than subluminal motion. The heatwave is a manifestation of an accretion burst.