White dwarf planetary debris dependence on physical structure distributions within asteroid belts

TL;DR

This paper develops an analytical model to understand how the physical shape and composition of asteroids influence their disruption around white dwarfs, affecting debris distribution based on white dwarf temperature and asteroid structure.

Contribution

It introduces a new framework for modeling triaxial asteroid disruption near white dwarfs, improving upon spherical models and linking white dwarf cooling age to debris outcomes.

Findings

Elongated asteroids are more likely to sublimate before disruption.

Fragmentation occurs at the largest semi-axis, regardless of shape.

White dwarf temperature influences the dominant disruption process.

Abstract

White dwarfs which exhibit transit signatures of planetary debris and accreted planetary material provide exceptional opportunities to probe the material composition and dynamical structure of planetary systems. Although previous theoretical work investigating the role of minor body disruption around white dwarfs has focussed on spherical bodies, Solar System asteroids can be more accurately modelled as triaxial ellipsoids. Here we present an analytical framework to identify the type of disruption (tidal fragmentation, total sublimation or direct impact) experienced by triaxial asteroids approaching white dwarfs on extremely eccentric (e \sim 1) orbits. This framework is then used to identify the outcomes for simplified Main belt analogues of 100 bodies across five different white dwarf temperatures. We also present an empirical relationship between cooling age and effective temperature for both DA and DB white dwarfs to identify the age of the white dwarfs considered here. We find that using a purely spherical shape model can underestimate the physical size and radial distance at which an asteroid is subjected to complete sublimation, and these differences increase with greater elongation of the body. Contrastingly, fragmentation always occurs in the largest semi-axis of a body and so can be modelled by a sphere of that radius. Both fragmentation and sublimation are greatly affected by the body's material composition, and hence by the composition of their progenitor asteroid belts. The white dwarf temperature, and hence cooling age, can affect the expected debris distribution: higher temperatures sublimate large elongated asteroids, and cooler temperatures accommodate more direct impacts.