Star Formation and the Hall Effect

TL;DR

This paper presents a semi-analytic model showing that the Hall effect significantly influences star formation by affecting magnetic diffusion, shock formation, and potentially inducing rotation in collapsing molecular cloud cores.

Contribution

It introduces a self-similar model incorporating Hall and ambipolar diffusion, revealing the Hall effect's profound impact on collapse dynamics and disc formation.

Findings

Hall diffusion influences magnetic and centrifugal shocks.

Hall effect can induce rotation in non-rotating cores.

Hall diffusion affects magnetic braking and field diffusion.

Abstract

Magnetic fields play an important role in star formation by regulating the removal of angular momentum from collapsing molecular cloud cores. Hall diffusion is known to be important to the magnetic field behaviour at many of the intermediate densities and field strengths encountered during the gravitational collapse of molecular cloud cores into protostars, and yet its role in the star formation process is not well-studied. This thesis describes a semianalytic self-similar model of the collapse of rotating isothermal molecular cloud cores with both Hall and ambipolar diffusion, presenting similarity solutions that demonstrate that the Hall effect has a profound influence on the dynamics of collapse. ... Hall diffusion also determines the strength of the magnetic diffusion and centrifugal shocks that bound the pseudo and rotationally-supported discs, and can introduce subshocks that further slow accretion onto the protostar. In cores that are not initially rotating Hall diffusion can even induce rotation, which could give rise to disc formation and resolve the magnetic braking catastrophe. The Hall effect clearly influences the dynamics of gravitational collapse and its role in controlling the magnetic braking and radial diffusion of the field would be worth exploring in future numerical simulations of star formation.