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We have observed the low-mass molecular cloud core G204.4-11.3A2-NE (G204NE) in the direction of Orion B giant molecular cloud with the Atacama Large Millimeter/submillimeter Array in Band 6. The 1.3 mm continuum images and visibilities unveil a compact central structure with a radius of ∼12 au, while showing no signature of binarity down to 18 au. The bolometric temperature and luminosity of this source are derived to be ∼33 K and ∼1.15 L⊙, respectively. Chemical stratification is observed in dense gas tracers, with C18O emission peaking at the continuum position surrounded by the spatially extended emission of N2D+ and DCO+. This implies that the core is in a very early evolutionary stage in which CO depletion occurs in most regions except for a small area heated by the central source. The envelope kinematics indicate a rotating and infalling structure with a central protostar mass of 0.08–0.1 M⊙. The protostar drives a collimated outflow traced by CO, SiO, SO, and H2CO, with misaligned blueshifted and redshifted lobes exhibiting a pair of bow-like patterns. High-velocity jets, extending up to 720 au, are detected in CO, SiO, and SO lines. The jet launching region is likely within twice of the dust sublimation zone. The absence of a binary signature suggests the outflows and jets are driven by a single protostar, although a close binary cannot be ruled out. The observed deflection of the outflows and jet is likely due to turbulent accretion in a moderately magnetized core.

Jets can facilitate the mass accretion onto the protostars in star formation. They are believed to be launched from accretion disks around the protostars by magnetocentrifugal force, as supported by the detections of rotation and magnetic fields in some of them. Here we report a radial flow of the textbook-case protostellar jet HH 212 at the base to further support this jet-launching scenario. This radial flow validates a central prediction of the magnetocentrifugal theory of jet formation and collimation, namely, the jet is the densest part of a wide-angle wind that flows radially outward at distances far from the (small, sub-au) launching region. Additional evidence for the radially flowing wide-angle component comes from its ability to reproduce the structure and kinematics of the shells detected around the HH 212 jet. This component, which can transport material from the inner to outer disk, could account for the chondrules and Ca–Al-rich inclusions detected in the solar system at large distances.

Protostellar outflows and jets are almost ubiquitous characteristics during the mass accretion phase and encode the history of stellar accretion, complex organic molecule (COM) formation, and planet formation. Episodic jets are likely connected to episodic accretion through the disk. Despite the importance, studies on episodic accretion and ejection links have not been done yet in a systematic fashion using high-sensitivity and high-resolution observations. To explore episodic accretion mechanisms and the chronologies of episodic events, we investigated 39 fields containing protostars with Atacama Large Millimeter/submillimeter Array observations of CO, SiO, and 1.3 mm continuum emission. We detected SiO emission in 19 fields, where 17 sources are driving molecular jets. Jet velocities, mass-loss rates, mass accretion rates, and periods of accretion events appear to have some dependence on the driving forces of the jet (e.g., bolometric luminosity, envelope mass). Next, velocities and mass-loss rates appear to be somewhat correlated with the surrounding envelope mass, suggesting that the presence of high mass around protostars increases the ejection–accretion activity. We determine mean periods of ejection events of 20–175 yr for our sample, which could be associated with perturbation zones of ∼2−25 au extent around the protostars. In addition, mean ejection periods show an apparent anticorrelation with the envelope mass, where high accretion rates may trigger more frequent ejection events. The observed periods of outburst/ejection are much shorter than the freezeout timescale of the simplest COMs like CH3OH, suggesting that episodic events could affect the ice–gas balance inside and around the snowline.

A first hydrostatic core (FHC) is proposed to form after the initial collapse of a prestellar core, as a seed of a Class 0 protostar. FHCs are difficult to observe because they are small, compact, embedded, and short lived. In this work, we explored the physical properties of two well-known FHC candidates, B1-bN and B1-bS, by comparing interferometric data from Submillimeter Array (SMA) 1.1 and 1.3 mm and Atacama Large Millimeter/submillimeter Array (ALMA) 870 μm observations with simulated synthesis images of the two sources. The simulated images are based on a simple model containing a single, hot compact first-core-like component at the center surrounded by a large-scale, cold and dusty envelope described by a broken power-law density distribution with an index, α. Our results show that the hot compact components of B1-bN and B1-bS can be described by temperatures of ∼500 K with a size of ∼4 au, which are in agreement with theoretical predictions of an FHC. If the α inside the broken radii is fixed to −1.5, we find α ∼−2.9 and ∼−3.3 outside the broken radii for B1-bN and B1-bS, respectively, consistent with theoretical calculations of a collapsing, bounded envelope and previous observations. Comparing the density and temperature profiles of the two sources with radiation-hydrodynamic simulations of an FHC, we find both sources lie close to, but before, the second collapse stage. We suggest that B1-bS may have started the collapsing process earlier compared to B1-bN, since a larger discontinuity point is found in its density profile.

Prestellar cores represent the initial conditions of star formation, but heavy molecules such as CO are strongly depleted in their cold, dense interiors, limiting the ability to probe core centers. Deuterated molecular ions therefore emerge as key tracers because deuterium fractionation is enhanced at low temperatures. We present the first direct observation of ortho-H2D+ depletion in the prestellar core G205.46−14.56 M3 using ALMA 820 μm continuum and ortho-H2D+ (110–111) data at ∼300 au resolution. We confirm the previously reported two substructures, B1 and B2, and identify a central ortho-H2D+ depletion zone toward B1 with ∼6σ contrast and an inferred diameter ≲600 au, together with a peak x(N2D+)/x(N2H+) = 1.03−0.56+0.07 . The observationally inferred profiles of x(ortho-H2D+) and x(N2D+)/x(N2H+) are reproduced by a deuteration-focused chemodynamical model; however, the central o-H2D+ depletion is only marginally matched within the 2σ upper limit, likely suggesting additional deuteration in the depletion zone. From these models we infer a core age of ∼0.42 Ma, comparable to the freefall time, suggesting that the substructures formed via rapid, turbulence-dominated fragmentation rather than slow, quasistatic contraction. Our observations also reveal that ortho-H2D+ velocity dispersions are largely subsonic in the core and nearly thermal between B1 and B2, consistent with turbulence dissipating within a few freefall times. These results highlight the critical role of deuterated ions for both chemical evolution and dynamics in dense cores.

Star formation is a series of mass assembly processes and starless cores; those cold and dense condensations in molecular clouds play a pivotal role as initial seeds of stars. With only a limited sample of known starless cores, however, the origin and growth of such stellar precursors had not been well characterized previously. Meanwhile, the recent discovery of CH3OH emission, which is generally associated with the desorbed icy mantle in warm regions, particularly at the periphery of starless cores, also remains puzzling. We present sensitive Atacama Large Millimeter/submillimeter Array (Band 3) observations (at 3 mm) toward a sample of newly identified starless cores in the Orion molecular cloud. The spatially resolved images distinctly indicate that the observed CH3OH and N2H+ emission associated with these cores are morphologically anticorrelated and kinematically offset from each other. We postulate that the CH3OH emission highlights the desorption of icy mantle by shocks resulting from gas piling onto dense cores in the filaments traced by N2H+. Our magnetohydrodynamic simulations of star formation in turbulent clouds combined with radiative transfer calculations and imaging simulations successfully reproduced the observed signatures and reaffirmed the above scenario at work. Our result serves as an intriguing and exemplary illustration, a snapshot in time, of the dynamic star-forming processes in turbulent clouds. The results offer compelling insights into the mechanisms governing the growth of starless cores and the presence of gas-phase complex organic molecules associated with these cores.

Protostellar jets are one of the most intriguing signposts in star formation. Recent detection of a jet rotation indicates that they can carry away angular momenta from the innermost edges of the disks, allowing the disks to feed the central protostars. In current jet-launching models, magnetic fields are required to launch and collimate the jets, however, observationally, it is still uncertain if magnetic fields are really present in the jets. Here we report a clear detection of SiO line polarization in the HH 211 protostellar jet. Since this line polarization has been attributed to the Goldreich-Kylafis effect in the presence of magnetic field, our observations show convincingly the presence of magnetic field in a jet from a low-mass protostar. The implied magnetic field could be mainly toroidal, as suggested in current jet-launching models, in order to collimate the jet at large distances. The presence of magnetic fields in protostellar jets has been predicted theoretically, but its experimental confirmation has been elusive so far. Here, the authors report the detection of SiO line polarisation in the HH 211 protostellar jet, indicative of the onset of magnetic fields.

The presence of complex organic molecules (COMs) in the interstellar medium is of great interest since it may link to the origin and prevalence of life in the universe. Aiming to investigate the occurrence of COMs and their possible origins, we conducted a chemical census toward a sample of protostellar cores as part of the Atacama Large Millimeter/submillimeter Array Survey of Orion Planck Galactic Cold Clumps project. We report the detection of 11 hot corino sources, which exhibit compact emissions from warm and abundant COMs, among 56 Class 0/I protostellar cores. All of the hot corino sources discovered are likely Class 0, and their sizes of the warm region (>100 K) are comparable to 100 au. The luminosity of the hot corino sources exhibits positive correlations with the total number of methanol and the extent of its emissions. Such correlations are consistent with the thermal desorption picture for the presence of hot corinos and suggest that the lower-luminosity (Class 0) sources likely have a smaller region with COM emissions. With the same sample selection method and detection criteria being applied, the detection rates of the warm methanol in the Orion cloud (15/37) and the Perseus cloud (28/50) are statistically similar when the cloud distances and the limited sample size are considered. Observing the same set of COM transitions will bring a more informative comparison between the cloud properties.

Complex organic molecules (COMs) in starless cores provide critical insights into the early stages of star formation and prebiotic chemistry. We present a chemical survey of 16 starless cores (including five prestellar cores) in the Orion A and B molecular clouds, targeting CH3OH, N2H+, CCS, and c-C3HD, using the Atacama Compact Array (ACA) and the Yebes 40 m telescope. CH3OH was detected toward all targets, confirming its ubiquity in starless cores, consistent with previous surveys in Taurus and Perseus. ACA imaging shows that CH3OH, CCS, and c-C3HD generally trace the outer layers of the dense cores outlined by N2H+, each exhibiting distinct spatial distributions. Meanwhile, comparison with Yebes data reveals an extended, flattened CH3OH component. CCS and c-C3HD tend to be detected or nondetected together across cores, while cores near dust-rich regions on a large scale often lack both, suggesting environmental influences linked to the interstellar radiation field. Within individual cores, CCS typically resides in an outer layer relative to c-C3HD. Our findings underscore the importance of high-resolution studies for understanding the origins and spatial differentiation of COMs and carbon-chain molecules in cold, quiescent environments.

In clustered star-forming regions, stellar feedback, such as H ii regions/photon-dominated regions (PDRs), and protostellar jets/outflows, shapes cloud structures and influences star formation. Using high-resolution Atacama Large Millimeter/submillimeter Array millimeter and JWST infrared data, we analyze the cloud structure and the impact of stellar feedback in the nearest dense cluster-forming region Ophiuchi (Oph) A. All six known Class 0/I and two of the six flat-spectrum/Class II objects are detected in the 1.3 mm dust continuum. Additionally, we newly detected seven substellar cores, three of which show compact near-infrared emission, suggesting they are young substellar objects. The remaining cores, with masses of ∼10−2 M⊙ and mean densities of ∼108 cm−3, are likely gravitationally bound. They appear connected by faint CO finger-like structures extending from the triple Class 0 system Very Large Array (VLA) 1623-2417 Aa+Ab+B, suggesting they may have been ejected from the close binary VLA 1623 Aa+Ab. 12CO and near-infrared data reveal multiple protostellar outflows. From the comparison, we identified several new outflows/jets and shocked structures associated with the GSS 30 large bipolar bubble. Strong 12CO emission traces the eastern edge of the Oph A ridge, forming part of the expanding H ii/PDR bubble driven by the nearby Herbig Be star S1. The northern ridge appears “blown out,” with warm gas flowing toward GSS 30, injecting additional turbulent momentum. Several C18O striations in the S1 bubble align with magnetic fields, and position–velocity diagrams show wave-like patterns, possibly reflecting magnetohydrodynamic waves. Stellar feedback significantly influences Oph A’s cloud structure.