The Formation of Discs in the Interior of AGB Stars from the Tidal Disruption of Planets and Brown Dwarfs

TL;DR

This paper simulates how planets and brown dwarfs are tidally disrupted inside AGB stars, forming accretion discs that could explain the origin of strong magnetic fields in white dwarfs.

Contribution

It provides hydrodynamic simulations of tidal disruption and disc formation inside AGB stars, a novel approach to understanding magnetic field origins in white dwarfs.

Findings

Disrupted companions form accretion discs consistent with previous estimates.

Discs are capable of generating strong magnetic fields in white dwarfs.

Tidal disruption events are a plausible source of magnetic field origins.

Abstract

A significant fraction of isolated white dwarfs host magnetic fields in excess of a MegaGauss. Observations suggest that these fields originate in interacting binary systems where the companion is destroyed thus leaving a singular, highly-magnetized white dwarf. In post-main-sequence evolution, radial expansion of the parent star may cause orbiting companions to become engulfed. During the common envelope phase, as the orbital separation rapidly decreases, low-mass companions will tidally disrupt as they approach the giant's core. We hydrodynamically simulate the tidal disruption of planets and brown dwarfs, and the subsequent accretion disc formation, in the interior of an asymptotic giant branch star. These dynamically formed discs are commensurate with previous estimates, suggesting strong magnetic fields may originate from these tidal disruption events.