Post-main-sequence debris from rotation-induced YORP break-up of small bodies

TL;DR

This paper proposes that the YORP effect during stellar evolution causes small bodies to break apart, creating debris that contributes to the dusty discs observed around white dwarfs.

Contribution

It introduces a model where stellar radiation during giant phases induces spin-up and breakup of small bodies, explaining debris around white dwarfs.

Findings

Small bodies 100 m - 10 km are destroyed within 7 au during giant phases.

Debris can extend to thousands of au, forming discs around white dwarfs.

YORP-induced breakup explains observed polluted white dwarf discs.

Abstract

Although discs of dust and gas have been observed orbiting white dwarfs, the origin of this circumstellar matter is uncertain. We hypothesize that the in-situ breakup of small bodies such as asteroids spun to fission during the giant branch phases of stellar evolution provides an important contribution to this debris. The YORP effect, which arises from radiation pressure, accelerates the spin rate of asymmetric asteroids, which can eventually shear themselves apart. This pressure is maintained and enhanced around dying stars because the outward push of an asteroid due to stellar mass loss is insignificant compared to the resulting stellar luminosity increase. Consequently, giant star radiation will destroy nearly all bodies with radii in the range 100 m - 10 km that survive their parent star's main sequence lifetime within a distance of about 7 au; smaller bodies are spun apart to their strongest, competent components. This estimate is conservative, and would increase for highly asymmetric shapes or incorporation of the inward drag due to giant star stellar wind. The resulting debris field, which could extend to thousands of au, may be perturbed by remnant planetary systems to reproduce the observed dusty and gaseous discs which accompany polluted white dwarfs.