Abstract

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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Data availability

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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Acknowledgements

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.

Author information

Affiliations

  1. Star and Planet Formation Laboratory, RIKEN Cluster for Pioneering Research, Wako-shi, Saitama, Japan

    • Yichen Zhang
  2. Department of Space, Earth and Environment, Chalmers University of Technology, Gothenburg, Sweden

    • Jonathan C. Tan
  3. Department of Astronomy, University of Virginia, Charlottesville, VA, USA

    • Jonathan C. Tan
    •  & Mengyao Liu
  4. Department of Earth and Space Science, Osaka University, Toyonaka, Osaka, Japan

    • Kei E. I. Tanaka
  5. ALMA Project, National Astronomical Observatory of Japan, Tokyo, Japan

    • Kei E. I. Tanaka
  6. SOFIA-USRA, NASA Ames Research Center, Moffett Field, CA, USA

    • James M. De Buizer
  7. INAF — Osservatorio Astrofisico di Arcetri, Firenze, Italy

    • Maria T. Beltrán
  8. Department of Astronomy and Steward Observatory, University of Arizona, Tucson, AZ, USA

    • Kaitlin Kratter
  9. Departamento de Astronomía, Universidad de Chile, Santiago, Chile

    • Diego Mardones
    •  & Guido Garay

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Contributions

Y.Z. led part of the ALMA observations, performed the data analysis, led the discussions and drafted the manuscript. J.C.T. led part of the ALMA observation, and participated in the discussions and drafting manuscript. K.E.I.T. contributed to the discussions. The rest of the authors discussed the results and commented on the manuscript.

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The authors declare no competing interests.

Corresponding author

Correspondence to Yichen Zhang.

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    Supplementary text, Supplementary references, Supplementary Figures 1–6.

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https://doi.org/10.1038/s41550-019-0718-y