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A protostellar system fed by a streamer of 10,500 au length


Binary formation is an important aspect of star formation. One possible route for close-in binary formation is disk fragmentation1,2,3. Recent observations show that small-scale asymmetries (<300 au) around young protostars2,4, although not always resolving the circumbinary disk, are linked to disk phenomena5,6. In later stages, resolved circumbinary disk observations7 (<200 au) show similar asymmetries, suggesting that the asymmetries arise from binary–disk interactions8,9,10. We observed one of the youngest systems to study the connection between disk and dense core. We find a bright and clear streamer in chemically fresh material (carbon-chain molecular species) that originates from outside the dense core (>10,500 au). This material connects the outer dense core with the region where asymmetries arise near disk scales. This new structure type, ten times larger than those seen near disk scales, suggests a different interpretation of previous observations: large-scale accretion flows funnel material down to disk scales. These results reveal the under-appreciated importance of the local environment on the formation and evolution of disks in early systems11,12 and a possible initial condition for the formation of annular features in young disks13,14.

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Fig. 1: NOEMA and ALMA observations of Per-emb-2.
Fig. 2: Streamer traced by HC3N J = 10→9 emission.
Fig. 3: Sky position and velocity along the line of sight of the streamline model overlaid on the observations.

Data availability

The data and analysis that support the findings of this study are available in GitHub (repository with the identifier


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J.E.P. thanks A. Burkert, A. A. Goodman, S. S. R. Offner and R. S. Klessen for discussions and comments. Observations were carried out with the IRAM interferometer NOEMA. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). This paper makes use of the following ALMA data: ADS/JAO.ALMA\#2013.1.00031.S. 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. This research made use of Astropy, a community-developed core Python package for Astronomy, and APLpy, an open-source plotting package for Python hosted at

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Authors and Affiliations



J.E.P. led the project and reduced the ALMA data, led the project and imaged the NOEMA data. N.C. and R.N. reduced the NOEMA data. J.E.P. wrote the manuscript. All authors contributed to the NOEMA proposal, discussed the results and implications and commented on the manuscript.

Corresponding author

Correspondence to Jaime E. Pineda.

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The authors declare no competing interests.

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Peer review information Nature Astronomy thanks Charles Hull and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Ratio of the integrated intensity of HC3N (10-9) to (8-7) transitions as a function of H2 density.

The ratio is calculated using RADEX, for kinetic temperatures of 10 and 12.25 K in blue and red, respectively. The measured average value and associated uncertainty of the ratio in the streamer is marked by the horizontal solid and dashed lines, respectively. This comparison shows that the average density in the streamer is (4±2) × 104 cm−3.

Extended Data Fig. 2 The streamer is unrelated to the old inner (radius <3,000 au) envelope or to the outflow emission from the young protostellar system.

Comparison between HC3N emission tracing the streamer and “chemically old” dense gas in panels a and b, and with the outflow in panel c. Panels a and b show the dense gas traced by N2H+ and N2D+ in the background, with the contours of the chemically fresh material. The streamer is clearly mostly outside the N2H+ and N2D+ emission, and it shows a significantly different morphology to the inner envelope. Panel c shows the outflow emission traced by CO (2-1) in red and blue contours, while the background emission is the HC3N integrated intensity. This shows that the streamer is unrelated to the outflow interaction. The 50% primary beam response for the N2H+, N2D+, and CO (2-1) observations are shown by the white dotted circle in the left and right panels, respectively. The HC3N contours levels are drawn at 5, 8, 11, 14 and 17x rms, where rms is 8 mJy beam−1 km s−1. The CO contours levels are drawn at 5, 15, 25, 35 and 45x rms, where rms is 0.2 Jy beam−1 km s−1.

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Pineda, J.E., Segura-Cox, D., Caselli, P. et al. A protostellar system fed by a streamer of 10,500 au length. Nat Astron 4, 1158–1163 (2020).

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