First steps of planet formation around very low mass stars and brown dwarfs

Abstract

Brown dwarfs and very low mass stars are a significant fraction of stars in our galaxy and they are interesting laboratories to investigate planet formation in extreme conditions of low temperature and densities. In addition, the dust radial drift of particles is expected to be a more difficult barrier to overcome during the first steps of planet formation in these disks. ALMA high-angular resolution observations of few protoplanetary disks around BDs and VLMS have shown substructures as in the disks around Sun-like stars. Such observations suggests that giant planets embedded in the disks are the most likely origin of the observed substructures. However, this type of planets represent less than 2% of the confirmed exoplanets so far around all stars, and they are difficult to form by different core accretion models (either pebble or planetesimal accretion). Dedicated deep observations of disks around BDs and VLMS with ALMA and JWST will provide significant progress on understanding the main properties of these objects (e.g., disk size and mass), which is crucial for determining the physical mechanisms that rule the evolution of these disks and the effect on the potential planets that may form in these environments.

Small and Large Dust Cavities in Disks around Mid-M Stars in Taurus

“…However, only little is known about substructures in disks around mid-to late M stars. Most structured disks around M dwarf stars show rings and gaps (González-Ruilova et al 2020;Cieza et al 2021;Kurtovic et al 2021;Pinilla et al 2021;van der Marel et al 2022), where the gaps are mostly central cavities or large gaps surrounding a compact inner disk (Pinilla 2022). Only one disk around a mid-M dwarf shows a clear asymmetric ring, with properties similar to asymmetries found around T Tauri and Herbig AeBe stars (Hashimoto et al 2021).…”

Effects of environment and multiplicity on planet formation

“…Looking at discs with large cavities in their dust distribution, van der Marel [12] describes how these can be related to the presence of low-mass companions, such as planets. Conversely, Pinilla [13] focuses the discussion on the effects of dust evolution and planet formation on discs around very low mass stars and brown dwarfs. Finally, Emsenhuber et al [14] take the final step of connecting the current knowledge of planet formation, with its complexity in outcome, with some cluster properties.…”

A Large Double-ring Disk Around the Taurus M Dwarf J04124068+2438157

“…Currently, most high-resolution observations are designed to target disks around early-type stars (M3 or earlier) and/or bright disks (that also mostly surround solar-mass stars, see references above). Though gaps and rings have been reported in the disks of a few bright M dwarfs (Hashimoto et al 2021;Kurtovic et al 2021;Pinilla 2022), our generic knowledge about dust substructure properties in disks around these latetype stars is still missing. In addition, we expect that the dust radial drift problem is even more severe for disks around lower mass stars, as the drift velocity is faster when surrounding lower mass stars (…”