Global Non-ideal Magnetohydrodynamic Simulations of Protoplanetary Disks with Outer Truncation

Abstract

It has recently been established that the evolution of protoplanetary disks is primarily driven by magnetized disk winds, requiring large-scale magnetic flux threading the disks. The size of such disks is expected to shrink in time, as opposed to the conventional scenario of viscous expansion. We present the first global 2D non-ideal magnetohydrodynamic (MHD) simulations of protoplanetary disks that are truncated in the outer radius, aiming to understand the interaction of the disk with the interstellar environment, as well as global evolution of the disk and magnetic flux. We find that as the system relaxes, poloidal magnetic field threading the disk beyond the truncation radius collapses towards the midplane, leading to rapid reconnection. This process removes a substantial amount of magnetic flux from the system, and forms closed poloidal magnetic flux loops encircling the outer disk in quasisteady-state. These magnetic flux loops can drive expansion beyond truncation radius, corresponding to substantial mass loss through magnetized disk outflow beyond truncation radius analogous to a combination of viscous spreading and external photoevaporation. The magnetic flux loops gradually shrink over time whose rates depend on level of disk magnetization and external environments, which eventually governs the long-term disk evolution.

Natural separation of two primordial planetary reservoirs in an expanding solar protoplanetary disk

“…Such observations show that some disks display a relatively high α 10 −3 −0.1 (35,36), compatible with measurements from non-ideal MHD disk simulations (34). Moreover, a recent study found that even in the magnetized wind-driven disk where the MRI is fully quenched, the magnetic torque can also drive the expansion of the gas in the outer disk region, analogous to the viscous spreading effect (37). This implies that our expanding disk scenario can be applicable for a broad range of circumstances.…”

Natural separation of two primordial planetary reservoirs in an expanding solar protoplanetary disk

“…Such observations show that some disks display a relatively high  ≳ 10 −3 − 0.1 (35,36), compatible with measurements from nonideal MHD disk simulations (34). Moreover, a recent study found that, even in the magnetized winddriven disk where the MRI is fully quenched, the magnetic torque can also drive the expansion of the gas in the outer disk region, analogous to the viscous spreading effect (37). This implies that our expanding disk scenario can be applicable for a broad range of circumstances.…”

Gas Disk Sizes from CO Line Observations: A Test of Angular Momentum Evolution

“…In the alternative magneto-hydrodynamical (MHD) disk wind model, angular momentum is transported in the wind, moving vertically away from the disk (Blandford & Payne 1982;Ferreira 1997;Gressel et al 2015;Bai et al 2016). That behavior can result in a more radially compact gas density distribution (e.g., Lesur 2021;Yang & Bai 2021). Comparing disk sizes in a large sam-ple that spans a range of evolutionary stages could help differentiate between the two scenarios.…”