Multiple protostellar outflows from a single protostar with a misaligned disk

Abstract

We investigate how misalignment between the core angular momentum and the large-scale magnetic field affects protostellar outflows, and whether a single protostellar system can drive multiple outflow components. We perform three-dimensional nonideal magnetohydrodynamic simulations of magnetized rotating cores, focusing on the formation of a protostar, a circumstellar disk, and magnetically driven outflows. The initial angle between the core angular-momentum vector and the magnetic field is systematically varied from $0^\circ$ to $90^\circ$. All models launch a classical magnetocentrifugal disk wind (DW) roughly along the local disk normal. For large misalignment, the system also develops a spiralflow (SF) component that propagates parallel to the disk plane. In a representative model with a $60^\circ$ misalignment, the outflow transitions from a DW-dominated to an SF-dominated phase, with the SF becoming more massive and more extended than the DW, and the two components intermittently coexisting. Across the model suite, the maximum mass and size ratios of SF to DW, as well as the relative lifetimes of the two components, increase for misalignment angles $\gtrsim60^\circ$. We propose that secondary, misaligned outflows (or their fossil remnants) observed in some protostellar systems can be interpreted as the SF component, while the main bipolar outflow traces the DW from the same misaligned system.

Figures (6)

• Figure 1: Three-dimensional structure of the magnetized protostellar system in the misaligned model T60 with an initial angle of $\theta_0 = 60^\circ$. We show the density contours of the disk (blue), the disk wind (DW; yellow), and the spiralflow component (SF; red). The white lines show the magnetic field lines.
• Figure 2: Time evolution of the outflow properties in the misaligned model T60. Panel (a): Masses of the protostar, circumstellar disk, disk wind (DW), and spiralflow (SF) components as functions of the time after protostar formation, $t_{\rm ps}$. Panel (b): Corresponding characteristic extents of the DW and SF, where $z_{\rm DW}$ is the maximum vertical distance along the disk axis and $r_{\rm SF}$ is the maximum radial distance in the disk plane. In both panels, the colored background indicates phases during which each outflow component is strongly present: blue, red, and green shading correspond to periods when the DW mass, the SF mass, and both components simultaneously exceed a fiducial threshold of $10^{-3}\,M_\odot$, respectively, using the same criterion as in Figure \ref{['fig:theta-values']}(b).
• Figure 3: Time evolution of the outflow properties for all misalignment models T00--T90. This figure generalizes the single-model evolution shown in Figure \ref{['fig:tps-values']} to the full range of misalignment angles and provides the time-series data from which the summary diagnostics in Figure \ref{['fig:theta-values']} are derived.
• Figure 4: Mass fractions of the circumstellar components (disk, DW, and SF) as functions of the protostellar mass for models T00--T90 (from top to bottom).
• Figure 5: Dependence of the relative importance of the SF component on the initial misalignment angle $\theta_0$. Panel (a): Maximum mass ratio $(M_{\rm SF}/M_{\rm DW})_{\max}$ and maximum size ratio $(r_{\rm SF}/z_{\rm DW})_{\max}$ attained during the evolution for models T00--T90. The horizontal gray line indicates unity. Panel (b): Fractional durations of the simulation during which the DW mass, the SF mass, and both components simultaneously exceed a fiducial threshold of $10^{-3}\,M_\odot$. The red, blue, and green filled regions indicate, respectively, the fractions of the simulated time for which DW, SF, and both components are "on", using the same mass threshold as in Figures \ref{['fig:tps-values']}(b) and \ref{['fig:tps-values_T00-90']}(b).