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 size due
to their different tensile strengths, and the largest maximum size corresponds
to 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 $a_{p}\le$ 25 nm, but large composite grains would be destroyed if the
particles are large with $a_{p}\ge 50$ 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 located in
regions with slightly higher gas density and weaker radiation intensity than
the average ISM.
