The loss of mass from protostars, in the form of a jet or outflow, is a necessary counterpart to protostellar mass accretion1,2. Outflow ejection events probably vary in their velocity and/or in the rate of mass loss. Such ‘episodic’ ejection events3 have been observed during the class 0 protostellar phase (the early accretion stage)4,5,6,7,8,9,10, and continue during the subsequent class I phase that marks the first one million years of star formation11,12,13,14. Previously observed episodic-ejection sources were relatively isolated; however, the most common sites of star formation are clusters15. Outflows link protostars with their environment and provide a viable source of the turbulence that is necessary for regulating star formation in clusters3, but it is not known how an accretion-driven jet or outflow in a clustered environment manifests itself in its earliest stage. This early stage is important in establishing the initial conditions for momentum and energy transfer to the environment as the protostar and cluster evolve. Here we report that an outflow from a young, class 0 protostar, at the hub of the very active and filamentary Serpens South protostellar cluster16,17,18, shows unambiguous episodic events. The 12C16O (J = 2−1) emission from the protostar reveals 22 distinct features of outflow ejecta, the most recent having the highest velocity. The outflow forms bipolar lobes—one of the first detectable signs of star formation—which originate from the peak of 1-mm continuum emission. Emission from the surrounding C18O envelope shows kinematics consistent with rotation and an infall of material onto the protostar. The data suggest that episodic, accretion-driven outflow begins in the earliest phase of protostellar evolution, and that the outflow remains intact in a very clustered environment, probably providing efficient momentum transfer for driving turbulence.
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A.L.P. is supported by a National Science Foundation (NSF) Graduate Research Fellowship under grant DGE-1122492; this research was made possible by the US Student Program of Fulbright Chile. H.G.A. receives funding from the NSF under grant AST-0845619. D.M. acknowledges support from CONICYT project PFB-06. M.M.D. acknowledges support from the Submillimeter Array through a postdoctoral fellowship. ALMA is a partnership of the European Space Organization (ESO, representing its member states), NSF (USA) and National Institutes of Natural Sciences (Japan), together with the National Research Council (Canada) and National Security Council and Academia Sinica Institute of Astronomy and Astrophysics (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, Associated Universities Inc. (AUI)/National Radio Astronomy Observatory (NRAO) and National Astronomical Observatory of Japan. The NRAO is a facility of the NSF, operated under cooperative agreement by AUI. This paper makes use of the following ALMA data: ADS/JAO.ALMA 2012.1.00769.S.
The authors declare no competing financial interests.
Extended data figures and tables
Extended Data Figure 1 C18O emission from the protostellar source C7.
Top row, blueshifted emission; bottom row, redshifted emission; velocity increases from left to right. Contours begin at 4σ and increment by 4σ. Specific velocity ranges (|VLSR − Vc|, or velocity relative to cloud velocity) are given for each column. Each panel shows integrated emission from two channels. The location of peak continuum emission is marked with a magenta cross.
Extended Data Figure 2 1-mm continuum emission near the sources CARMA-7 (RA = 18 h 30 min 04.1 s, dec. = −02° 03′ 02.6″) and CARMA-6 (RA = 18 h 30 min 03.5 s, dec. = −02° 03′ 08.4″).
Contours show 10σ, 30σ, 50σ and 70σ, followed by increments of 50σ. Near these strong sources, we find the r.m.s. noise to be 0.3 mJy beam−1.
Extended Data Figure 3 Cartoon depiction of a protostellar system, showing the outflow (12CO emission), envelope (C18O emission) and disk (unresolved).
Contributions to blueshifted and redshifted molecular line emission are indicated along the outflow and envelope, assuming that the outflow is nearly in the plane of the sky with respect to the observer.
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Plunkett, A., Arce, H., Mardones, D. et al. Episodic molecular outflow in the very young protostellar cluster Serpens South. Nature 527, 70–73 (2015). https://doi.org/10.1038/nature15702
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