Complex Structure around a Circumstellar Disk Caused by Interchange Instability

TL;DR

This study uses advanced 3D nonideal MHD simulations to reveal how interchange instability causes complex, long-lasting structures around forming stars, aligning with recent observations and highlighting magnetic flux removal during star formation.

Contribution

First long-term 3D nonideal MHD simulation without a sink cell showing interchange instability effects on circumstellar structures.

Findings

Interchange instability causes recurrent ring, arc, and cavity structures.

Magnetic flux accumulates at disk edges, driving instability.

Disk growth continues despite instability, with evolving outflows.

Abstract

We perform a three-dimensional nonideal magnetohydrodynamic simulation of a strongly magnetized cloud core and investigate the complex structure caused by the interchange instability. This is the first simulation that does not use a central sink cell and calculates the long term ($> 10^4$ yr) evolution even as the disk and outflow formation occur. The magnetic field dissipates inside the disk, and magnetic flux accumulates around the edge of the disk, leading to the occurrence of interchange instability. During the main accretion phase, the interchange instability occurs recurrently, disturbing the circumstellar region and forming ring, arc, and cavity structures. These are consistent with recent high-resolution observations of circumstellar regions around young protostars. The structures extend to $>1,000$ au and persist for at least 30,000 yr after protostar formation, demonstrating the dynamic removal process of magnetic flux during star formation. We find that the disk continues to grow even as interchange instability occurs, by accretion through channels between the outgoing cavities. The outflow is initially weak, but becomes strong after $\sim 10^3$ yr.