Early planet formation in embedded protostellar disks

Abstract

Recent surveys of young star formation regions have shown that the dust mass of the average class II object is not high enough to make up the cores of giant planets. Younger class O/I objects have enough dust in their embedded disk, which raises the question whether the first steps of planet formation occur in these younger systems. The first step is building the first planetesimals, which are generally thought to be the product of the streaming instability. Hence the question can be restated to read whether the physical conditions of embedded disks are conducive to the growth of the streaming instability. The streaming instability requires moderately coupled dust grains and a dust-to-gas mass ratio near unity. We model the collapse of a dusty proto-stellar cloud to show that if there is sufficient drift between the falling gas and dust, regions of the embedded disk can become sufficiently enhanced in dust to drive the streaming instability. We include four models to test a variety of collapse theories: three models with different dust grain sizes, and one model with a different initial cloud angular momentum. We find a sweet spot for planetesimal formation for grain sizes of a few 10s of micron because they fall sufficiently fast relative to the gas to build a high dust-to-gas ratio in the disk midplane, but their radial drift speeds are slow enough in the embedded disk to maintain the high dust-to-gas ratio. Unlike the gas, which is held in hydrostatic equilibrium for a time as a result of gas pressure, the dust can begin to collapse from all radii at a much earlier time. The dust mass flux in class O/I systems can thus be higher than the gas flux. This builds an embedded dusty disk with a global dust-to-gas mass ratio that exceeds the inter-stellar mass ratio by at least an order of magnitude. The streaming instability can produce at least between 7 and 35 M⊕ of planetesimals in the class O/I phase of our smooth embedded disks, depending on the size of the falling dust grains. This mass is sufficient to build the core of the first giant planet in the system, and could be further enhanced by dust traps and/or pebble growth. This first generation of planetesimals could represent the first step in planet formation. It occurs earlier in the lifetime of the young star than is traditionally thought.

A Millimeter-multiwavelength Continuum Study of VLA 1623 West

“…Planets form and evolve in protoplanetary disks around young stars. Recent insights from simulations and observations of young disk masses have suggested an early onset for dust growth leading to planetesimal formation in the Class 0/I protostellar disk phase (Tychoniec et al 2020;Cridland et al 2022;Drazkowska et al 2022). Early imprints of this process at work could explain the substructure of two possible rings and gaps at tens of astronomical units seen in the young Class I protostar, IRS 63 (Segura-Cox et al 2020).…”

What does a typical full-disc around a post-AGB binary look like? -- Radiative transfer models reproducing PIONIER, GRAVITY, and MATISSE data

“…It has now been well established that this property of the SEDs provides observational evidence for the presence of stable, massive circumbinary discs around these systems (e.g. de Ruyter et al 2006;Van Winckel 2003, 2017; Ka-Based on observations collected at the European Southern Observatory under ESO programmes 094.D-0865, 0102.D-0760, 60.A-9275, and 0104.D-0739 math et al 2014Kluska et al 2022). Observational properties of these systems were recently reviewed by Van Winckel (2018).…”

“…While there is growing evidence that initial phases of planet formation around YSOs can be short and that grain growth is very efficient on short timescales (∼ 10 5 yr; e.g. Sheehan & Eisner 2018;Segura-Cox et al 2020;Cridland et al 2022;Lau et al 2022), it is as yet unclear what the formation timescale of fullgrown planets is. Discs around post-AGB binaries, thus, represent an interesting laboratory for testing processes for planet formation, and this in a different parameter space than around YSOs.…”

“…IRAS 08544 is a luminous (∼ 10500 L ) post-AGB star with a confirmed companion (Maas et al 2003). The binary is surrounded by an optically thick circumbinary disc; its near-IR excess provides evidence for a full disc, with the inner rim located at the dust sublimation radius (de Ruyter et al 2006;Hillen et al 2016;Kluska et al 2018;Kluska et al 2022). It is classified as a Category 1 disc in Kluska et al (2022) and is the prototypical full disc surrounding a post-AGB binary.…”

A millimeter-multiwavelength continuum study of VLA 1623 West

“…Planets form and evolve in protoplanetary disks around young stars. Recent insights from simulations and observations of young disk masses have suggested an early onset for dust growth leading to planetesimal formation in the Class 0/I protostellar disk phase (Tychoniec et al 2020;Cridland et al 2022;Drazkowska et al 2022). Early imprints of this process at work could explain the substructure of two possible rings and gaps at tens of au seen in the young Class I protostar, IRS 63 (Segura-Cox et al 2020).…”