Radiation pressure mixing of large dust grains in protoplanetary disks

TL;DR

This paper proposes that infrared radiation pressure in protoplanetary disks can loft large dust grains outward, facilitating the mixing of crystalline grains from hot inner regions to colder outer regions, explaining observed grain compositions.

Contribution

It introduces a novel mechanism where infrared radiation pressure transports large grains across the disk, offering an alternative to traditional mixing theories.

Findings

Infrared radiation can loft grains larger than one micrometre.

Lofted grains are pushed outward by stellar radiation pressure.

Process may be active in most young stellar objects and brown dwarfs.

Abstract

Dusty disks around young stars are formed out of interstellar dust that consists of amorphous, submicrometre grains. Yet the grains found in comets and meteorites, and traced in the spectra of young stars, include large crystalline grains that must have undergone annealing or condensation at temperatures in excess of 1,000 K, even though they are mixed with surrounding material that never experienced temperatures as high as that. This prompted theories of large-scale mixing capable of transporting thermally altered grains from the inner, hot part of accretion disks to outer, colder disk region, but all have assumptions that may be problematic. Here I report that infrared radiation arising from the dusty disk can loft grains bigger than one micrometre out of the inner disk, whereupon they are pushed outwards by stellar radiation pressure while gliding above the disk. Grains re-enter the disk at radii where it is too cold to produce sufficient infrared radiation pressure support for a given grain size and solid density. Properties of the observed disks suggest that this process might be active in almost all young stellar objects and young brown dwarfs.