Abstract:
We present a model for the formation of silicon carbide aggregates within the expanding and cooling supernova
remnant. SiC type-X (SiC-X) grains measured in the laboratory at a high spatial resolution have been found
to be aggregates of smaller crystals which are isotopically homogenous. The initial condensation of SiC in the
ejecta occurs within an interior dense shell of material which is created by a reverse shock which rebounds
from the core–envelope interface. A subsequent reverse shock accelerates the grains forward, but the gas drag
from the ejecta on the rapidly moving particles limits their travel distance. By observing the effects of gas drag
on the travel distance of grains, we propose that supernova grain aggregates form from material that condensed
in a highly localized region, which satisfies the observational evidence of isotopic homogeneity in SiC-X grains.
