Rotational disruption of dust grains by radiative torques in strong radiation fields

Massive stars, supernovae, and kilonovae are among the most luminous radiation sources in the Universe. Observations usually show near- to mid-infrared (NIR–MIR, λ ≈？1–5？μm) emission excess from H？ii regions around young massive star clusters. Early-phase observations in optical-to-NIR wavelengths of type Ia supernovae also reveal unusual properties of dust extinction and dust polarization. The most common explanation for such NIR？MIR excess and unusual dust properties is the predominance of small grains (size a？？？0.05？μm) relative to large grains (a？？？0.1？μm) in the local environment of these strong radiation sources. However, why small grains might be predominant in these environments is unclear. Here we report a mechanism of dust destruction based on centrifugal stress within extremely fast-rotating grains spun-up by radiative torques, which we term radiative torque disruption (RATD). We find that RATD can disrupt large grains located within a distance of about a parsec from a massive star of luminosity L？≈？104L⊙, where L⊙ is the solar luminosity, or from a supernova. This disruption effect increases the abundance of small grains relative to large grains and successfully reproduces the observed NIR？MIR excess and anomalous dust extinction/polarization. We apply the RATD mechanism for kilonovae and find that dust within about 0.1 parsec would be dominated by small grains. Small grains produced by RATD can also explain the steep far-ultraviolet rise in extinction curves towards starburst and high-redshift galaxies, and the decrease of the escape fraction of Lyman α photons from H？ii regions surrounding young massive star clusters