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

TL;DR

This study presents high-resolution observations of Cepheus A, revealing that gravity primarily drives gas flows, with magnetic fields regulating turbulence and aligning across multiple scales, challenging traditional views of magnetic resistance.

Contribution

It provides the first detailed multiscale analysis showing gravity-driven flows and magnetic field regulation in a massive protostellar cluster, with implications for star formation theories.

Findings

Gravity induces gas flows dragging magnetic fields.

Magnetic tension regulates turbulence and supports ordered flows.

Magnetic fields are coherently aligned across multiple spatial scales.

Abstract

The hierarchical interplay among gravity, magnetic fields, and turbulence in forming massive protostellar clusters remains elusive. We present high-resolution ($\sim$14 arcsec $\simeq$ 0.05 pc) 850 $\mu$m 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 $E_{\mathrm{G}}$ > $E_{\mathrm{B}}$ > $E_{\mathrm{K}}$. 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 $\sim$ 2.1 $\pm$ 0.4 $\times$ 10$^{-4}$ M$_\odot$ yr$^{-1}$. This challenges the conventional view of B-fields resisting collapse in the clump/hub scale, instead showing cooperation with gravity. The $\sim$0.6 pc clump-scale B-field (with mean PA $\sim$ 45{\deg}) aligns coherently with fields at cloud ($\sim$5 pc), core ($\sim$0.05 pc), and disk ($\sim$2000 AU) scales, offering new insights into the role of magnetic fields in multiscale star formation dynamics.