Hall-magnetohydrodynamic simulations of X-ray photoevaporative protoplanetary disc winds

TL;DR

This study uses advanced 2D MHD simulations to explore how the Hall Effect influences X-ray driven winds and accretion in protoplanetary disks, revealing the magnetic field's role in disk dispersal and mass loss.

Contribution

It combines non-ideal MHD effects with thermochemistry in simulations, highlighting the impact of the Hall Effect on disk wind dynamics and mass loss rates.

Findings

Hall Effect causes inward displacement of poloidal magnetic fields.

Magnetic fields influence mass loss rates, especially at low X-ray luminosities.

Wind mass loss converges to hydrodynamic predictions at high X-ray luminosities.

Abstract

Understanding the complex evolution of protoplanetary disks (PPDs) and their dispersal via energetic stellar radiation are prominent challenges in astrophysics. It has recently been established that specifically the X-ray luminosity from the central protostar can significantly heat the surface of the disk, causing powerful photoevaporative winds that eject a considerable fraction of the disc's mass. Recent work in the field has moreover shown the importance of global PPD simulations that simultaneously take into account non-ideal magnetohydrodynamic (MHD) effects and detailed thermochemistry. Our motivation with the current paper lies in combining these two aspects and figure out how they interact. Focus is put on the Hall Effect (HE) and the impact it has on the overall field topology and mass loss/accretion rates. Utilizing a novel X-ray temperature parametrisation, we perform 2D-axisymmetric MHD simulations with the NIRVANA fluid code, covering all non-ideal effects. We find that, in the aligned orientation, the HE causes prominent inward displacement of the poloidal field lines that can increase the accretion rate through a laminar Maxwell stress. We find that outflows are mainly driven by photoevaporation -- unless the magnetic field strength is considerable (i.e., $\beta_p\leq 10^{3}$) or the X-ray luminosity low enough (i.e., $\log{L_X}\leq 29.3$). Inferred mass loss rate are in the range of the expected values $10^{-8}$ to $10^{-7}M_{\odot}yr^{-1}$. For comparison, we have also performed pure hydrodynamic (HD) runs and compared them with the equivalent MHD runs. Here we have found that the magnetic field does indeed contribute to the mass loss rate, albeit only discernibly so for low enough $L_X$ (i.e., $\log{L_X}\leq 30.8$). For values higher than that, the wind mass loss predicted from the MHD set converges to the ones predicted from pure HD.