Almost all massive stars have bound stellar companions, existing in binaries or higher-order multiples1,2,3,4,5. While binarity is theorized to be an essential feature of how massive stars form6, essentially all information about such properties is derived from observations of already formed stars, whose orbital properties may have evolved since birth. Little is known about binarity during formation stages. Here we report high-angular-resolution observations of 1.3 mm continuum and H30α recombination line emission, which reveal a massive protobinary with apparent separation of 180 au at the centre of the massive star-forming region IRAS 07299-1651. From the line-of-sight velocity difference of 9.5 km s−1 of the two protostars, the binary is estimated to have a minimum total mass of 18 solar masses, consistent with several other metrics, and maximum period of 570 yr, assuming a circular orbit. The H30α line from the primary protostar shows kinematics consistent with rotation along a ring of radius of 12 au. The observations indicate that disk fragmentation at several hundred astronomical units may have formed the binary, and much smaller disks are feeding the individual protostars.
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This paper makes use of the following ALMA data: ADS/JAO.ALMA#2015.1.01454.S, ADS/JAO.ALMA#2016.1.00125.S. The data are available at https://almascience.nao.ac.jp/aq by setting the observation codes. The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
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The authors thank N. Sakai for valuable discussions. ALMA is a partnership of ESO (representing its member states), NSF (United States) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Y.Z. acknowledges support from RIKEN Special Postdoctoral Researcher Program. J.C.T. acknowledges support from NSF grant AST1411527 and ERC Advanced Grant project MSTAR. K.E.I.T. acknowledges support from NAOJ ALMA Scientific Research Grant Number 2017-05A. D.M. and G.G. acknowledge support from CONICYT project Basal AFB-170002.
The authors declare no competing interests.
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Zhang, Y., Tan, J.C., Tanaka, K.E.I. et al. Dynamics of a massive binary at birth. Nat Astron 3, 517–523 (2019). https://doi.org/10.1038/s41550-019-0718-y