Here we present deep ( 16 \mu Jy beam ^ { -1 } ) , very high ( 40 mas ) angular resolution 1.14 mm , polarimetric , Atacama Large Millimeter/submillimeter Array ( ALMA ) observations towards the massive protostar driving the HH 80-81 radio jet .
The observations clearly resolve the disk oriented perpendicular to the radio jet , with a radius of \simeq 0 \farcs 171 ( \sim 291 au at 1.7 kpc distance ) .
The continuum brightness temperature , the intensity profile , and the polarization properties clearly indicate that the disk is optically thick for a radius of R \la 170 au .
The linear polarization of the dust emission is detected almost all along the disk and its properties suggest that dust polarization is produced mainly by self-scattering .
However , the polarization pattern presents a clear differentiation between the inner ( optically thick ) part of the disk and the outer ( optically thin ) region of the disk , with a sharp transition that occurs at a radius of \sim 0 \farcs 1 ( \sim 170 au ) .
The polarization characteristics of the inner disk suggest that dust settling has not occurred yet with a maximum dust grain size between 50 and 500 \mu m. The outer part of the disk has a clear azimuthal pattern but with a significantly higher polarization fraction compared to the inner disk .
This pattern is broadly consistent with self-scattering of a radiation field that is beamed radially outward , as expected in the optically thin outer region , although contribution from non-spherical grains aligned with respect to the radiative flux can not be excluded .