Is grain growth taking place around the Cosmic Pretzel?

Carolina Agurto-Gangas, Laura Perez, Anibal Sierra, Felipe Alves, Paola Caselli

Observational and modeling contraints of when the growth of dust grains from sub-micrometer to millimeter sizes occurs, is crucial to understand the planet formation process. This provides the first step towards the production of pebbles and planetesimals in protoplanetary disks.
Currently, it is well established that Class II disks have large dust grains. However, it is not clear how early in the star formation process this grain growth occurs. In order to expand the study of grain growth in young disks, we decide to model the dust properties in the outer and inner regions of the Class I protostar binary BHB07-11, or better known as the Cosmic Pretzel. For this purpose, we used the multi-wavelength ?30 au resolution ALMA observations in Band 3, 6 and 7 to determine whether there are spatial variations in the grain size distribution. The analysis provides constraints on surface density and maximum grain size as a function of radius, and suggests a variation in dust grain properties between disk-inner-envelope and that dust grains have grown from an initial ISM-like dust population. Additionally, Toomre Q parameter is close to or below 1.7 at large radii (>150au), indicative of a marginally gravitationally unstable system, and in well agreement with the observed spiral arm structure in all the bands.