Energetic Protons, Radionuclides and Magnetic Activity in Protostellar Disks

TL;DR

This study models the ionization and magnetic activity in protostellar disks, revealing persistent dead and undead zones that influence disk turbulence and magnetic field generation.

Contribution

It provides a comprehensive analysis of ionization sources and their impact on dead zone locations, introducing the concept of undead zones with intermediate resistivities.

Findings

Dead zones exist in most ionization scenarios.

Undead zones with large-scale magnetic fields are common.

Mass columns in undead zones often exceed 1000 g/cm^2.

Abstract

We calculate the location of the magnetically-inactive dead zone in the minimum-mass protosolar disk, under ionization scenarios including stellar X-rays, long- or short-lived radionuclide decay, and energetic protons arriving from the general interstellar medium, from a nearby supernova explosion, from the disk corona, or from the corona of the young star. The disk contains a dead zone in all scenarios except those with small dust grains removed and a fraction of the short-lived radionuclides remaining in the gas. All the cases without exception have an "undead zone" where intermediate resistivities prevent magneto-rotational turbulence while allowing shear-generated large-scale magnetic fields. The mass column in the undead zone is typically greater than the column in the turbulent surface layers. The results support the idea that the dead and undead zones are robust consequences of cold, dusty gas with mass columns exceeding 1000 g/cm^2.