The Impact of Silicate Grain Coagulation on Millimeter Emission from Massive Protostellar Disks

Abstract

Hot accretion disks around massive protostars provide a unique opportunity to study ice-free silicate grains that cannot be investigated in protoplanetary disks. We conduct a self-consistent investigation into grain-size evolution and its impact on (sub)millimeter-wave emission from massive protostellar disks. Our radiative transfer modeling accounts for dust self-scattering and includes vertical temperature gradients in the disk structure. The results show that once silicate grains grow to sizes exceeding the observing wavelength, enhanced scattering dims the disk emission by 20\%--30\% relative to the blackbody emission expected at the disk surface temperature. By comparing our model with Atacama Large Millimeter/submillimeter Array 1.14 mm observations of the disk around the massive protostar GGD27-MM1, we constrain the threshold velocity for collisional fragmentation of silicate grains to approximately 15 m s-1. This fragmentation velocity is lower than the typical maximum collisional velocities in protoplanetary disks around low-mass stars, suggesting that collisional coagulation alone is insufficient for silicate dust to form rocky planetesimals in such environments. Furthermore, our analysis identifies two potential scenarios to better reproduce the bright inner-disk emission of GGD27-MM1. One possibility is that the grain growth is limited to 160 mum by another growth barrier (e.g., collisional bouncing), reducing scattering dimming. Alternatively, the stellar luminosity may be as much as five times higher than current estimates, compensating for the reduced brightness. Future multiwavelength observations, particularly at shorter submillimeter wavelengths, will be crucial to distinguish between these scenarios and further constrain silicate grain coagulation processes in massive protostellar disks.

20 pages, 8 figures,accepted for publication to The Astrophysical Journal

References in corpus (18)

• Dust size distributions in coagulation/fragmentation equilibrium: Numerical solutions and analytical fits
• One Solution to the Mass Budget Problem for Planet Formation: Optically Thick Disks with Dust Scattering
• The anomalously low (sub)millimeter spectral indices of some protoplanetary disks may be explained by dust self-scattering
• Sticking Properties of Silicates in Planetesimal Formation Revisited
• The Impact of Feedback During Massive Star Formation by Core Accretion
• Spiral arms and instability within the AFGL 4176 mm1 disc
• An analytical model of radial dust trapping in protoplanetary disks
• Fractal aggregates of sub-micron-sized grains in the young planet-forming disk around IM Lup
• Non-linear Development of Secular Gravitational Instability in Protoplanetary Disks
• Evolution of the Water Snow Line in Magnetically Accreting Protoplanetary Disks
• Drifting inwards in protoplanetary discs II: The effect of water on sticking properties at increasing temperatures
• The first bird's-eye view of a gravitationally unstable accretion disk in high-mass star formation
• Support for fragile porous dust in a gravitationally self-regulated disk around IM Lup
• Modeling the accretion disk around the high-mass protostar GGD 27-MM1
• Cohesion of regolith: Measurements of meteorite powders
• The circumestellar disk of the B0 protostar powering the HH 80-81 radio jet
• Massive Protostars in a Protocluster -- A Multi-Scale ALMA View of G35.20-0.74N
• Massive Protostellar Disks as a Hot Laboratory of Silicate Grain Evolution