The young protostellar disc in IRAS 16293−2422 B is hot and shows signatures of gravitational instability

Abstract

Deeply embedded protostars are actively fed from their surrounding envelopes through their protostellar disk. The physical structure of such early disks might be different from that of more evolved sources due to the active accretion. We present 1.3 and 3 mm ALMA continuum observations at resolutions of 6.5 au and 12 au respectively, towards the Class 0 source IRAS 16293-2422 B. The resolved brightness temperatures appear remarkably high, with Tb > 100 K within ∼30 au and Tb peak over 400 K at 3 mm. Both wavelengths show a lopsided emission with a spectral index reaching values less than 2 in the central ∼ 20 au region. We compare these observations with a series of radiative transfer calculations and synthetic observations of magnetohydrodynamic and radiation hydrodynamic protostellar disk models formed after the collapse of a dense core. Based on our results, we argue that the gas kinematics within the disk may play a more significant role in heating the disk than the protostellar radiation. In particular, our radiation hydrodynamic simulation of disk formation, including heating sources associated with gravitational instabilities, is able to generate the temperatures necessary to explain the high fluxes observed in IRAS 16293B. Besides, the low spectral index values are naturally reproduced by the high optical depth and high inner temperatures of the protostellar disk models. The high temperatures in IRAS 16293B imply that volatile species are mostly in the gas phase, suggesting that a self-gravitating disk could be at the origin of a hot corino.

Testing a New Model of Embedded Protostellar Disks Against Observation: The Majority of Orion Class 0/I Disks Are Likely Warm, Massive, and Gravitationally Unstable

“…Such asymmetry is clearly visible in Fig. 15 and has been observed, for example, in the small Class 0 disk in IRAS 16293 B (Zamponi et al 2021). Note that both examples here have relatively small disks, and theoretically GIinduced asymmetry should be less significant for larger disks.…”

No Evidence of the Significant Grain Growth but Tentative Discovery of Disk Substructure in a Disk around the Class I Protostar L1489 IRS

“…Several observations have suggested that the dust grains have already significantly grown at the Class 0/I stage (e.g., Kwon et al 2009;Zhang et al 2015;Cieza et al 2016;Harsono et al 2018) even though these observations may be affected by the high optical depth. In contrast, recent observations toward a protostellar disk of IRAS 16293-2422 B have suggested that the dust grains may not become larger (a max 10 μm; Zamponi et al 2021). Therefore, it is important to understand how and when the dust grains are grown by revealing the spatial distribution of both the initial ISM's dust and larger dust grains in protostellar disks with optically thin dust emission.…”

Formation of Dust Clumps with Sub-Jupiter Mass and Cold Shadowed Region in Gravitationally Unstable Disk around Class 0/I Protostar in L1527 IRS

“…Dust temperature has been investigated in protoplanetary disks using various molecular lines (e.g., Kamp & Dullemond 2004;Notsu et al 2020;Liu et al 2021;Öberg et al 2021). It has recently been suggested that the temperature in Class 0/I disks is hotter than that in Class II protoplanetary disks (van 't Hoff et al 2018;Liu 2021;Zamponi et al 2021).…”