Direct evidence for magnetohydrodynamic disk winds driving rotating outflows in protostar HOPS 358

Abstract

Angular momentum removal is a fundamental requirement for star and planet formation, yet the mechanisms driving this process remain debated. Magnetohydrodynamic disk winds, launched along magnetic field lines from extended disk regions, offer a promising solution, particularly in regions where magnetorotational turbulence is weak. Here we present high-resolution Atacama Large Millimeter/submillimeter Array observations of the Class 0 protostar HOPS 358, revealing a rotating, nested outflow structure traced by H2CO, SO, and CH3OH emission. The outflow preserves the disk's rotational sense and is aligned with the disk axis, providing direct observational evidence for a magnetically launched disk wind. From the measured kinematics, we derive a dimensionless magnetic lever arm of approximately 2.3 and constrain the wind-launching region to radii of 10-18 astronomical units within the planet-forming zone. These results demonstrate that magnetohydrodynamic disk winds operate during the deeply embedded phase, efficiently extracting angular momentum while shaping disk evolution and establishing initial conditions for planet formation.

Figures (9)

• Figure 1: Integrated intensity and velocity maps of molecular lines tracing disk and outflows.a Integrated intensity (moment 0) and intensity-weighted velocity (moment 1) maps of molecular lines tracing the disk, together with a schematic illustration of the disk and outflow morphology in HOPS 358. b Moment 0 and moment 1 maps of molecular lines tracing outflows. The moment maps are constructed using only emission above 4$\sigma$$_{\text{mole}}$ within a velocity range of -11 to 11 km s$^{-1}$ with respect to systemic velocity, $v_{\text{sys}}$ = 11 km s$^{-1}$. The gray contours in each panel represent the 1.3 mm continuum emission at 10, 20, and 40$\sigma$$_{\text{cont}}$. Details of $\sigma_{\text{mole}}$ and $\sigma_{\text{cont}}$ are provided in Methods, subsection ALMA observations. The synthesized beam size corresponding to each molecular dataset is indicated by a black ellipse in the lower left corner of each moment 1 map. The illustration in the upper right presents a schematic view of a rotating disk and disk wind-driven outflows, retaining the same rotation feature as the disk. The orange solid line at each moment 1 map represents the jet/outflow axis (approximately 158$^{\circ}$). Colored rectangles in the moment 0 map of H$_2$CO indicate slices---centered at 0.05$^{\prime \prime}$, 0.15$^{\prime \prime}$, 0.25$^{\prime \prime}$, and 0.35$^{\prime \prime}$ from the disk mid-plane, each with a width of 0.1$^{\prime \prime}$---that are used to construct the corresponding transverse PV diagrams in Figure \ref{['fig:fig2']}.
• Figure 2: Transverse position-velocity diagrams of H$_2$CO emission across the outflow axis. Each slice position corresponding to the transverse PV diagrams is shown in the moment 0 map of H$_2$CO in Figure \ref{['fig:fig1']}. The value of z$_{\text{proj}}$ shown on each PV diagram indicates the central position of the respective slice. The colored dashed ellipse on each PV diagram represents the best-fit result from elliptical fitting. The purple and green dots correspond to the same reference points as those shown in Supplementary Fig. \ref{['extfig:SupplyFig1']}. Black contour levels correspond to 3, 6, and 9$\sigma$$_{\text{H$_{2}$CO}}$, while the magenta contour level corresponds to 2$\sigma$$_{\text{H$_{2}$CO}}$.
• Figure 3: Outflow properties derived from the PV diagrams of three molecular lines.a Outflow radius. The open symbols represent the outflow radius at z$_{\mathrm{proj}}$ = 0, $R_{0,\mathrm{geom}}$, estimated from parabolic fitting to the measured outflow radii for each molecule. The associated error bars indicate the 1$\sigma$ uncertainties of the $R_{0,\mathrm{geom}}$ derived from the covariance matrix of the parabolic fit. b Rotation velocity. c Specific angular momentum, $j = R_{\text{outflow}}\times v_{\phi}$. d Axial velocity. e Radial expansion velocity. f Poloidal (or outflowing) velocity. The red, orange, and blue markers represent the outflow properties derived from the H$_{2}$CO, CH$_{3}$OH, and SO molecular lines, respectively. Error bars represent the 1$\sigma$ statistical uncertainties propagated from the bootstrap-derived ellipse-fitting parameters. For the axial and poloidal velocities, which are particularly sensitive to the nearly edge-on geometry, the effect of inclination is illustrated by showing values computed for $i = 83^\circ$ and $87^\circ$, indicated by circle and triangle symbols, respectively. These values bracket the estimated inclination uncertainty of $85^{+2}_{-2}{^\circ}$.
• Figure 4: Comparison of observed outflow kinematics with theoretical MHD disk wind models. The outflow properties are normalized by the square root of the protostellar mass. The color scheme is the same as in Figure \ref{['fig:fig3']}; the red, orange, and blue symbols represent values derived from H$_{2}$CO, CH$_{3}$OH, and SO, respectively. Each symbol indicates the value calculated from the transverse PV diagram at the corresponding projected distance along the outflow axis from the disk, z$_{\text{proj}}$, assuming $i=85\hbox{$^{\circ}$}$. Error bars represent the 1$\sigma$ statistical uncertainties of the derived outflow properties, propagated from the bootstrap-derived ellipse-fitting parameters and including the inclination correction and mass normalization. The semi-transparent error bars indicate values recalculated assuming $i=83\hbox{$^{\circ}$}$ (left) and $i=87\hbox{$^{\circ}$}$ (right), illustrating the systematic effect of the inclination uncertainty. The curves represent the expected relations from steady self-similar MHD disk wind models. Solid curves correspond to different launching radii, $r_0$. Dashed curves correspond to different magnetic lever arm parameters, $\lambda_{\phi}$, which provide lower limits on the theoretical wind lever arm parameter.
• Figure 5: Spatial distribution of outflow-tracing molecular emission. The background image shows the dust continuum. The red contour represents the outer boundary of the moment 0 map of H$_{2}$CO emission, while the blue and orange contours show the moment 0 maps of SO and CH$_{3}$OH, respectively. Contour levels for each molecule correspond to 8.7 mJy Beam$^{-1}$ km s$^{-1}$ for H$_{2}$CO, 11.9 mJy Beam$^{-1}$ km s$^{-1}$ for SO, and 11.1 mJy Beam$^{-1}$ km s$^{-1}$ for CH$_{3}$OH, which represent two times the root mean square noise level of each moment 0 map.