Dust material in the clumpy ejecta of supernova remnants is exposed to high gas temperatures and shock velocities. On the one hand, the energetic conditions can cause a significant destruction of the dust grains due to sputtering or grain-grain collisions. On the other hand, the energetic gas ions can penetrate deep into the dust grains. For grain temperatures below ~500 K, the diffusion rate of oxygen and other heavy ions in silicates is very low and they are trapped once they have intruded into the grain. This process, named as ion trapping, has not been considered so far as a measure to counteract grain destruction by sputtering.
To study this phenomenon we considered a clump impacted by a shock-wave in the oxygen-rich supernova remnant Cassiopeia A. DiRAC HPC Facilities were used to conduct hydrodynamics simulations which were further post-processed with the code Paperboats (Kirchschlager et al. 2019). This allowed us to follow the dust mass and grain size evolution in the shocked ejecta material.
In our new study (Kirchschlager et al. 2020) we showed that penetration and trapping within silicate grains of oxygen, silicon, and magnesium, the same impinging ions that are responsible for grain surface sputtering, can significantly reduce the net loss of grain material (Fig. 1). We found for a pre-shock gas density contrast between clump and ambient medium of χ = 100 that ion trapping increases the surviving masses of silicate dust by factors of up to two to four, compared to cases where the effect is neglected (Fig. 2). The formation of grains larger than those that had originally condensed is facilitated and allows the presence of micrometre-sized grains in the post-shock medium. For higher density contrasts (χ ≥ 180), we found that the effect of gas accretion on the surface of dust grains surpasses ion trapping, and the survival rate increases to ∼55% of the initial dust mass for χ = 256.
Kirchschlager, Barlow, M. J., &
Schmidt, F. D. 2020, ApJ, 893, p.70-78