Ringed Disks Reveal Stokes Numbers of 10^{-4} to 10^{-2} and Low Turbulence in 10 Protoplanetary Systems
A new census of ringed disks more than doubles the number of systems with direct St and α measurements. Results indicate gas-rich conditions and inefficient planetesimal formation across diverse stellar hosts. The work highlights the need for deeper surveys of lower-mass disks to confirm the trend of leakier traps around M stars.
Researchers extended the Lee (2024) framework that couples the dust equation of motion with observed ring mass distributions to extract local St and α. The expanded sample of 19 rings in systems such as HL Tau and TW Hya shows consistently low values, implying gas-rich disks where dust-to-gas ratios remain below the threshold for direct planetesimal formation via streaming instability.
Low-mass host stars exhibit leakier traps, consistent with the observed scarcity of massive gap-carving giants around M dwarfs. This pattern suggests ring morphology encodes both microphysical dust properties and the dynamical influence of embedded planets, rather than pure pressure bumps from other mechanisms.
The findings align with ALMA surveys showing narrow rings but challenge models that assume higher turbulence to explain rapid grain growth. They also indicate that current ring samples are biased toward brighter, more massive disks, limiting extrapolation to the full population.
Next steps include targeted ALMA Band 6 observations of fainter Class I sources to test whether St remains uniformly low when ring contrast decreases, plus incorporation of multi-wavelength data to break the St–α degeneracy.
Lee: ALMA Cycle 12 data on 8 additional low-mass host rings will show mean St below 0.005 in at least 6 cases by 2028.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2609.00140)
- [2]Supporting Source(https://arxiv.org/abs/2405.12345)