Resolved Structure and Orbital Motion of a Localized 1 au-scale Dust Accumulation in the Protoplanetary Disk around TW Hya

The study uses high-resolution (~1 au) ALMA Band 6 dust continuum and 13CO and C18O J=2–1 emission-line observations of the TW Hya protoplanetary disk. Its main focus is the kinematics, internal morphology, and local gas environment of the prominent dust blob at a radius of 52 au.

By comparing 2021 data with archival 2017 observations, the authors detect the blob's proper motion. Its measured azimuthal velocity is 3.3±0.9 km/s, fully consistent with local Keplerian rotation. Combined with the lack of significant radial migration over the four-year baseline, this confirms that the structure is robustly co-moving with the disk system.

The high-resolution continuum map resolves the blob into a distinct double-peaked morphology separated by ~1.7 au azimuthally. The authors validate this double-peaked substructure by reproducing it in the independent 2017 dataset using a sparse-modeling image reconstruction technique.

They discuss potential physical origins for the double-peaked morphology, including an inclined circumplanetary disk with an inner dust cavity, the roots of planet-induced spiral arms, or alternative hydrodynamic scenarios that do not involve an actively accreting planet, such as the U-turn trajectory of secondary dust or a short-lived hydrodynamic gas vortex. They detect no compact gas emission counterparts associated with the continuum blob. Since the CO lines likely trace optically thick upper atmospheric layers, the absence of localized vertical gas perturbations suggests that if an embedded planet is responsible for the dust structure, its mass must be exceptionally low.