Probing the Physical Conditions of Supernova Ejecta with the Measured Sizes of Presolar Al2O3 Grains

TL;DR

This study investigates the formation conditions of large presolar Al2O3 grains from supernova ejecta, revealing that their sizes can constrain the dense gas environments where they formed, and introduces a new modeling approach.

Contribution

The paper introduces a non-dimensional parameter 'Lambda_on' to describe Al2O3 grain formation and shows large grains require denser gas than standard supernova models predict.

Findings

Large Al2O3 grains imply formation in dense gas clumps

'Lambda_on' effectively describes grain size and formation efficiency

Measured grain sizes can constrain supernova ejecta conditions

Abstract

A few particles of presolar Al2O3 grains with sizes above 0.5 mum are believed to have been produced in the ejecta of core-collapse supernovae (SNe). In order to clarify the formation condition of such large Al2O3 grains, we investigate the condensation of Al2O3 grains for wide ranges of the gas density and cooling rate. We first show that the average radius and condensation efficiency of newly formed Al2O3 grains are successfully described by a non-dimensional quantity "Lambda_on" defined as the ratio of the timescale with which the supersaturation ratio increases to the collision timescale of reactant gas species at dust formation. Then, we find that the formation of submicron-sized Al2O3 grains requires at least ten times higher gas densities than those presented by one-dimensional SN models. This indicates that presolar Al2O3 grains identified as a SN origin might be formed in dense gas clumps, allowing us to propose that the measured sizes of presolar grains can be a powerful tool to constrain the physical conditions in which they formed. We also briefly discuss the survival of newly formed Al2O3 grains against the destruction in the shocked gas within the SN remnants.