Patrick Koch (ASIAA)
We present 230 GHz continuum polarization observations with the Atacama Large Milimeter/Submillimeter Array (ALMA) at a resolution of 0.1" ( 540 au) in the high-mass star-forming regions W51 e2 and e8. These observations resolve a network of core-connecting filamentary extensions and fibers in dust continuum, marking a departure from earlier coarser roundish continuum structures. At the same time, the cores do not appear to fragment further. Polarized dust emission is clearly detected. The inferred magnetic field orientations are prevailingly parallel to extensions and fibers. This key structural feature is analyzed together with the local gravitational vector field. The direction of local gravity is found to typically align with extensions and fibers. With these findings we derive a stability criterion that defines a maximum magnetic field strength that can be overcome by an observed magnetic field-gravity configuration. Equivalently, this defines a minimum field strength that can stabilize extensions and fibers against a radial collapse. We find that the detected fibers and extensions in W51 e2 and e8 are stable, hence possibly making them a fundamental component in the accretion onto central cores. When comparing to coarser resolutions, covering the scales of envelope, global, and local collapse, we find recurring similarities in the magnetic field structures and their corresponding gravitational vector fields. These self-similar structures point at a multi-scale collapse-within-collapse scenario until finally the scale of core-accreting fibers is reached where gravity is entraining the magnetic field and aligning with fibers and extensions.