Evidence for the gravity-driven and magnetically regularized gas flows feeding the massive protostellar cluster in Cepheus A

The hierarchical interplay among gravity, magnetic fields, and turbulence in forming massive protostellar clusters remains elusive. We present high-resolution (~14 arc seconds ≃ 0.05 parsecs), 850-micrometer dust polarization and C 18 O line observations of Cepheus A using JCMT SCUBA-2/POL-2 and HARP. Our analysis reveals aligned gravitational (G), magnetic (B), and velocity fields (K), with an energy hierarchy of E G > E B > E K . Gravity, as the primary driver, induces gas flows and drags in B-field lines. Magnetic tension, as a secondary force, regulates turbulence, enabling ordered flows with an accretion rate of ~2.1 ± 0.4 × 10 −4 M ⊙ per year. This challenges the conventional view of B-fields resisting collapse in the clump/hub scale, instead showing cooperation with gravity. The ~0.6-parsec clump-scale B-field (with a mean position angle of ~45°) aligns coherently with fields at cloud (~5 parsecs), core (~0.05 parsecs), and disk (~2000 astronomical units) scales, offering key insights into the role of magnetic fields in multiscale star formation dynamics.