Salty Twin Disks in IRAS 16547-4247

Protostellar disks are one of the most fundamental components in star formation. Particularly in massive star formation, disks inside 100 au would be the key to solving the longstanding radiation pressure problem. One difficulty in disk observations around massive protostars is the lack of knowledge of which lines can trace the innermost region and separate the disk from the envelope. We report the results of the high-resolution ALMA observations of the O-type proto-binary system IRAS 16547-4247. We newly detect emission lines of sodium chloride (NaCl), silicon compounds (SiO, SiS), and vibrationally-excited water (H2O) as probes of the individual protostellar disks at a scale of 100 au. The presence of gaseous refractory species, which originate from the destruction of dust grains, and high-energy water vapor suggests the dynamic and hot nature of disks around massive protostars. This is the second detection of alkali metal halide in protostellar systems after the case of the disk of Orion Source I, and also one of few massive protostellar disks associated with high-energy water and silicon compounds. These new results suggest that those “hot-disk” lines may be common in innermost disks around massive protostars, and have great potential for future research of massive star formation. We also tentatively find that the twin disks are counter-rotating, which might provide a hint of the origin of the massive proto-binary system 16547-4247.