A Dynamical Constraint on Interstellar Dust Models from Radiative Torque Disruption

Interstellar dust is an essential component of the interstellar medium (ISM) and plays critical roles in astrophysics. Achieving an accurate model of interstellar dust is therefore of great importance. Interstellar dust models are usually built based on observational constraints such as starlight extinction and polarization, but dynamical constraints such as grain rotation are not considered. In this paper, we show that a newly discovered effect by Hoang et al., so-called RAdiative Torque Disruption (RATD), can act as an important dynamical constraint for dust models. Using this dynamical constraint, we derive the maximum size of grains that survive in the ISM for different dust models, including contact binary, composite, silicate core and amorphous carbon mantle, and compact grain model for the different radiation fields. We find that the different dust models have different maximum sizes due to their different tensile strengths, and the largest maximum size corresponds to the compact grains with the highest tensile strength. We show that the composite grain model cannot be ruled out if constituent particles are very small with radius a _p ≤ 25 nm, but large composite grains would be destroyed if the particles are large with a _p ≥ 50 nm. We suggest that grain internal structures can be constrained with observations using the dynamical RATD constraint for strong radiation fields such as supernova, nova, or star-forming regions. Finally, our obtained results suggest that micron-sized grains perhaps have compact/core-mantle structures or have composite structures but are located in regions with slightly higher gas density and weaker radiation intensity than the average ISM.