Protostellar Disks Fed By Dense Collapsing Gravo-Magneto-Sheetlets

TL;DR

This study uses non-ideal MHD simulations to reveal how dense gravo-magneto-sheetlets form during protostellar core collapse, serving as primary channels for mass and angular momentum transfer to disks, with magnetic fields playing a crucial role.

Contribution

It introduces the concept of dense gravo-magneto-sheetlets as key structures in protostellar envelope-to-disk mass transfer, highlighting magnetic field inheritance and its impact on disk evolution.

Findings

Dense sheetlets feed the disk mainly through their surfaces.

Disks inherit up to 10% of the envelope's magnetic flux.

Magnetic fields significantly influence disk angular momentum evolution.

Abstract

Stars form from the gravitational collapse of turbulent, magnetized molecular cloud cores. Our non-ideal MHD simulations reveal that the intrinsically anisotropic magnetic resistance to gravity during the core collapse naturally generates dense gravo-magneto-sheetlets within inner protostellar envelopes -- disrupted versions of classical sheet-like pseudodisks. They are embedded in a magnetically dominant background, where less dense materials flow along the local magnetic field lines and accumulate in the dense sheetlets. The sheetlets, which feed the disk predominantly through its upper and lower surfaces, are the primary channels for mass and angular momentum transfer from the envelope to the disk. The protostellar disk inherits a small fraction (up to 10\%) of the magnetic flux from the envelope, resulting in a disk-averaged net vertical field strength of 1-10 mG and a somewhat stronger toroidal field, potentially detectable through ALMA Zeeman observations. The inherited magnetic field from the envelope plays a dominant role in disk angular momentum evolution, enabling the formation of gravitationally stable disks in cases where the disk field is relatively well-coupled to the gas. Its influence remains significant even in marginally gravitationally unstable disks formed in the more magnetically diffusive cases, removing angular momentum at a rate comparable to or greater than that caused by spiral arms. The magnetically driven disk evolution is consistent with the apparent scarcity of prominent spirals capable of driving rapid accretion in deeply embedded protostellar disks. The dense gravo-magneto-sheetlets observed in our simulations may correspond to the ``accretion streamers" increasingly detected around protostars.