Grand Design Spiral Arms in A Young Forming Circumstellar Disk

TL;DR

This study uses resistive magnetohydrodynamic simulations to show that young circumstellar disks develop recurrent grand-design spiral arms due to gravitational instability, aligning well with recent observations of Elias 2-27.

Contribution

It demonstrates that recurrent spiral arms in young disks are caused by gravitational instability, providing a new understanding of disk evolution and angular momentum transfer.

Findings

Spiral arms form and recur throughout the Class-0 and I phases.

Simulated spiral arms match high-resolution observations of Elias 2-27.

Gravitational instability is key to angular momentum transport in young disks.

Abstract

We study formation and long-term evolution of a circumstellar disk in a collapsing molecular cloud core using a resistive magnetohydrodynamic simulation. While the formed circumstellar disk is initially small, it grows as accretion continues and its radius becomes as large as 200 AUs toward the end of the Class-I phase. A pair of grand-design spiral arms form due to gravitational instability in the disk, and they transfer angular momentum in the highly resistive disk. Although the spiral arms disappear in a few rotations as expected in a classical theory, new spiral arms form recurrently as the disk soon becomes unstable again by gas accretion. Such recurrent spiral arms persist throughout the Class-0 and I phase. We then perform synthetic observations and compare our model with a recent high-resolution observation of a young stellar object Elias 2-27, whose circumstellar disk has grand design spiral arms. We find good agreement between our theoretical model and the observation. Our model suggests that the grand design spiral arms around Elias 2-27 are consistent with material arms formed by gravitational instability. If such spiral arms commonly exist in young circumstellar disks, it implies that young circumstellar disks are considerably massive and gravitational instability is the key process of angular momentum transport.