Support for fragile porous dust in a gravitationally self-regulated disk around IM Lup

TL;DR

This paper presents a comprehensive physical model of the IM Lup protoplanetary disk, emphasizing the importance of fragile, porous dust in explaining multi-wavelength observations, millimeter polarization, and disk heating mechanisms.

Contribution

It introduces a unified model that accounts for diverse observations and highlights the role of dust fragility and porosity in disk evolution and planet formation processes.

Findings

Dust fragility is crucial for millimeter emission retention.

Moderately porous dust explains observed millimeter polarization.

Inner disk heating by gas accretion accounts for bright millimeter emission.

Abstract

Protoplanetary disks, the birthplace of planets, are expected to be gravitationally unstable in their early phase of evolution. IM Lup, a well-known T-Tauri star, is surrounded by a protoplanetary disk with spiral arms likely caused by gravitational instability. The IM Lup disk has been observed using various methods, but developing a unified explanatory model is challenging. Here we present a physical model of the IM Lup disk that offers a comprehensive explanation for diverse observations spanning from near-infrared to millimeter wavelengths. Our findings underscore the importance of dust fragility in retaining the observed millimeter emission and reveal the preference for moderately porous dust to explain observed millimeter polarization. We also find that the inner disk region is likely heated by gas accretion, providing a natural explanation for bright millimeter emission within 20 au. The actively heated inner region in the model casts a 100-au-scale shadow, aligning seamlessly with the near-infrared scattered light observation. The presence of accretion heating also supports the fragile dust scenario in which accretion efficiently heat the disk midplane. Due to the fragility of dust, it is unlikely that a potential embedded planet at 100 au formed via pebble accretion in a smooth disk, pointing to local dust enhancement boosting pebble accretion or alternative pathways such as outward migration or gravitational fragmentation.