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Abstract (Sub)millimeter dust polarization in protoplanetary disks has revealed the presence of large (∼100 μm) dust grains that are aligned along their long axis following the azimuthal direction of the disk. The novel badminton-birdie-like aerodynamic alignment predicts large grains to align with their long axes following the direction of gas flow experienced by the dust, denoted as theA-field. With 3D streaming instability (SI) simulations, we find that theA-field is predominantly in the radial direction in regions of low dust-to-gas ratio but in the azimuthal direction in regions of high dust-to-gas ratio. Through polarized radiation transfer, we find that the resulting polarization angle indeed follows the disk azimuthal direction in the high dust density regions. Therefore, ongoing SI is an attractive candidate for producing the azimuthal dust polarization pattern as observed in an increasing number of disks. 

Abstract Filamentary structures are ubiquitous in the interstellar medium, yet the extent to which magnetic fields influence the morphology of cold atomic gas remains an open question. The nearby Riegel–Crutcher cloud, composed of long and narrow Hifilaments observed in self-absorption, provides a critical test case. We present the most extensive optical polarimetric survey of this region to date, comprising more than 90,000 high signal-to-noise stellar polarization measurements combined with Gaia DR3 data. Using stellar polarization, extinction estimates, and archival Naiabsorption data, we locate the cloud at a distance of 150  ±  15 pc, consistent with that of the Pipe Nebula. The plane-of-sky magnetic field traced by optical starlight polarization closely matches that inferred independently from Planck 353 GHz dust-emission polarization, revealing a coherent large-scale magnetic field across the region. A Rolling Hough Transform analysis shows that the Hifilaments are tightly aligned with this field orientation. Together, these results provide strong observational evidence that the structure of the cold neutral medium in the Riegel–Crutcher cloud is closely linked to a highly ordered magnetic field. This level of coherence supports a scenario in which magnetic fields play a dynamically important role in shaping the cloud structure, and suggests that the Riegel–Crutcher cloud is part of a larger magnetized complex influencing gas flows in the solar neighborhood. 

Abstract Recent James Webb Space Telescope observations of Hii regions in the Central Molecular Zone (CMZ) have shown a highly filamentary morphology distinct from Hii regions in other parts of the Galaxy. We present magnetohydrodynamic (MHD) simulations of strongly magnetized (plasma-β ≪ 1) Hii region evolution that investigate and describe the formation of these ionized gas filaments. Hii region evolution has been simulated in a 30 pc³box, in distinct models with preplaced overdensities in the ambient medium and overdensities that have been generated with driven turbulence. We find that when these overdensities are seeded in the ambient medium before the birth of the ionizing source, the photoionized plasma stripped off of these dense blobs is funneled into long filaments along the magnetic field lines. The length and emission measure of these ionized gas filaments are similar to the filaments observed in the CMZ. Given that these filaments are effectively magnetically confined flows of photoionized gas, their density and curvature are influenced by the density of the blob and the geometry of the configuration. 

Abstract We performed numerical simulations along with radiative transfer calculations to reproduce an intriguing asymmetric shoulder feature in the dust-continuum emission of the protostellar disk around one of the eDisk targets, the Class 0 protostar IRAS 16544$$-$$1604 in CB 68. This is our first attempt to bridge the theoretical works of protostellar disk evolution and the eDisk observations. We found that while our hydrodynamic simulations form spiral structures caused by gravitational instability, they become less discernible after the disk is inclined and convolved with the telescope beam. The widths of the spiral structure as obtained by our numerical simulations are $${\sim }$$0.1–0.8 times the eDisk beam size of 4.5 au. Our modeling effort implies that the apparent absence of spiral features in the eDisk observations does not necessarily indicate the real absence of internal substructures and gravitational instability. We also found that the asymmetric shoulder structure of the continuum profile along the major axis appears when the disk is massive enough with a Toomre parameter $$Q\sim 1$$. This mechanism offers a potential explanation for the observed, asymmetric shoulder features in the disks surrounding IRAS 16544$$-$$1604 and the other eDisk sources. 

Abstract The origin of the jets in young stellar objects (YSOs) remains a subject of active investigation. We present a 3D MHD simulation of the jet launching in YSOs, focusing on the interaction between the stellar magnetosphere and the accretion disk. In our model, a fast low-density bipolar jet is powered by disk–magnetosphere interaction and launched through the polar cavity that is mass-loaded from the disk rather than the star. Specifically, outflows are driven by toroidal magnetic pressure generated along “two-legged” field lines, anchored at a magnetically dominated stellar footpoint and a mass-dominated point on the (magnetically elevated) disk surface via a cyclic “load–fire–reload” process: in the “load” stage, the differential rotation between the stellar and disk footpoints generates toroidal magnetic pressure; in the “fire” stage, vertical gradients in the toroidal field accelerate plasma and transport the Poynting flux into the polar cavity; and in the “reload” stage, magnetic reconnection allows the cycle to repeat, reforming “two-legged” field lines. These field lines are not required to be fully reset to a dipolar loop configuration; it is only required that the disk end be shallowly embedded in the (elevated) disk surface. This rapid asynchronous process produces a continuous large-scale outflow. The resulting magnetically dominated (Poynting) jet, accelerated by magnetic pressure within the low-density polar cavity, is distinct from the denser, slower disk wind launched through the classic magnetic tower mechanism. Comparison with a disk-only model shows that the rotating stellar magnetosphere promotesbipolarjet launching by shaping a magnetic geometry favorable to symmetric outflows. 

Abstract Recent discoveries of streamer-like structures around protostellar sources challenge the traditional picture of isolated, axisymmetric star formation. Here, we present new Atacama Large Millimeter/submillimeter Array observations of [BHB2007]-1, a flat-spectrum source connected to at least three such elongated structures. Two of these features are symmetrically located to the north and south of the disk, with velocities aligned with the disk on their respective sides. However, their unbound kinematics and curved morphology make it difficult to determine their origin. Possible explanations include outflows, interactions with the nearby [BHB2007]-2 system, and hyperbolic infall, but none fully account for all observed properties. In contrast, a newly identified collimated structure to the west shows clear evidence of gravitationally bound infall. Estimates of its mass, mass infall rate, and angular momentum suggest that this infalling streamer would roughly double the mass budget available to form planets and tilt the disk by a few tens of degrees. Furthermore, its misalignment with the midplane of the disk and the lack of diffuse envelope emission indicate that the streamer may have formed due to gravitational capture of cloud material unrelated to the source’s natal core. Together, these findings support a more dynamic picture of star formation, one where environmental interactions continue to shape the conditions for building planetary systems. 

Abstract Polarization-mode observations from the Atacama Large Millimeter/submillimeter Array (ALMA) are powerful tools for studying the dust grain populations in circumstellar disks. Many sources exhibit polarization signatures consistent with aligned dust grains, yet the physical origin of this alignment remains uncertain. One such source is BHB 07-11, a Class I protobinary object in the Pipe Nebula with complex spiral arm structures in its circumbinary disk. While magnetic fields are often invoked to explain grain alignment in the interstellar medium, the contrasting conditions in circumstellar disk environments demand further investigation into grain alignment mechanisms. To determine BHB 07-11’s dominant polarization mechanism, we leverage ALMA polarization-mode dust continuum observations in Bands 3 (λ = 3.1 mm), 6 (λ = 1.3 mm), and 7 (λ = 0.87 mm), in combination with high-resolution dust continuum and spectral line observations in Band 6. Observed polarization vectors in each band are consistent with emission from aligned grains and follow the structure of the spiral arms as shown in the high-resolution observations. Given the relationship between the observed polarization vector orientation and the spiral arms, we find that the polarization morphology is most consistent with grains aligned through a relative velocity flow between gas and dust in the spiral arms, as envisioned in the recently developed badminton birdie-like alignment mechanism, rather than alignment with a magnetic field or other known alignment mechanisms. 

Abstract As part of the ALMA Large Program “Early Planet Formation in Embedded Disks,”¹²CO (2–1) was observed towards 19 nearby low-mass protostars. Of these objects, 15 sources are found to show molecular outflow emission. Based on their morphological and kinematical structures, the CO outflows are classified into three types: a wind-driven shell, where ambient material is swept up by a wide-angle wind from the star, a bow shock, and a slow disk wind, which is a conical or parabolic flow with onion-like velocity structure. We categorize 11 outflows as a slow disk wind, 7 as a wind-driven shell, and 1 as a bow shock. Four of these outflows were found to show signs of both slow disk wind and wind-driven shell characteristics. Five objects show misalignment between the red- and blueshifted outflows. Seven objects show significant misalignment between the outflow axis (either or both of the red- and blueshifted outflows) and the minor axis of the dust continuum emission around the protostar. For the objects showing wind-driven shell emission, we compare simple parametrized models with the observations to derive physical properties of the observed shells, such as their dynamical ages. This shows evidence of a time variability in the outflows, such as changes in their direction. In some objects, large differences are seen between the properties of the red- and blueshifted outflows, possibly indicating differences in the properties of the ambient medium with which the outflow interacts. 

Abstract Magnetic braking can drive angular momentum loss in star formation and influence disk evolution. A previous study of HH 111 VLA 1 suggested a decrease in rotation velocity in a region between the infalling envelope and rotating disk. Using Atacama Large Millimeter/submillimeter Array C¹⁸O (J = 2–1) data, we analyzed the gas motion within 6000 au and found clear deviations from the simplest expectations of freefall toward the central star with conserved angular momentum in the transition region between the envelope and disk (from ∼5200 to 160 au). The region can be further divided into three zones: (1) outer region with a significant decrease in infall velocity, dropping to approximately 60% of the freefall velocity and 70% of conservation of angular momentum and energy; (2) middle region with a sharp drop in angular momentum and thus rotation velocity and an increase in infall velocity; and (3) inner region with rotation velocity increasing inward to connect to that of the Keplerian disk and infall velocity decreasing to zero. Comparison with nonideal MHD simulations suggests that the reduced infall velocity in the outer region can be due to magnetic tension by the pinched magnetic field lines, the sharp drop of angular momentum in the middle region can be due to magnetic braking as the field lines pileup, and the rapid increase in rotation velocity in the inner region might result from weaker magnetic braking due to ambipolar diffusion of the field lines. The resulting dip in the rotation profile supports magnetic braking. 

Abstract Magnetic fields influence the structure and evolution of protostellar systems; thus, understanding their role is essential for probing the earliest stages of star formation. We present Atacama Large Millimeter/submillimeter Array Band 3 and 6 polarized continuum observations at ∼0 $\stackrel{\text{″}}{.}$ 5 resolution toward the Class 0 protostellar system HH 211. Three dust filaments (∼4000 au in length) are found in the HH 211 protostellar envelope, two of which are aligned with core-scale (∼10,000 au) magnetic fields detected by previous James Clerk Maxwell Telescope observations. This result suggests that the formation of the dust filaments may be influenced by magnetic fields. In the inner envelope (∼1000 au), we detect a clear hourglass-shaped magnetic field morphology near the protostar and toroidal fields along the outflow directions. We also estimate the line-of-sight averaged temperature and column density distributions in the inner envelope and find that the temperature is higher in the east, while the column density is enhanced in the southern and western regions. The southern dense regions of the inner envelope may trace either outflow cavity walls, due to their alignment with the outflow, or possible infalling channels in the midplane, given the close correspondence between the observed magnetic fields and the predicted infall trajectories.