NanoSIMS, TEM, and XANES studies of a Unique Presolar Supernova Graphite Grain

TL;DR

This study uses NanoSIMS, TEM, and XANES techniques to analyze a unique presolar supernova graphite grain, revealing complex isotopic heterogeneities and a nanocrystalline core with novel structural features, shedding light on supernova ejecta processes.

Contribution

It reports the first nanocrystalline core in a low-density supernova graphite grain and details its microstructure and isotopic heterogeneities, advancing understanding of supernova dust formation.

Findings

Discovery of a nanocrystalline core with 2-4 nm graphene particles.

Identification of isotopic heterogeneities and shell-like structures.

Evidence for mixing and granular transport in supernova ejecta.

Abstract

We report on isotopic and microstructural investigations of a unique presolar supernova (SN) graphite grain, referred to as G6, isolated from the Orgueil CI chondrite. G6 contains complex heterogeneities in its isotopic composition and in its microstructure. Nano-scale secondary ion mass spectrometer isotope images of ultramicrotome sections reveal heterogeneities in its C, N, and O isotopic compositions, including anomalous shell-like structures. Transmission electron microscope studies reveal a nanocrystalline core surrounded by a turbostratic graphite mantle, the first reported nanocrystalline core from a low-density SN graphite grain. Electron diffraction analysis shows that the nanocrystalline core consists of randomly oriented 2-4 nm graphene particles, similar to those in cores of high-density (HD) presolar graphite grains from asymptotic giant branch stars. G6's core also exhibits evidence for planar stacking of these graphene nano-sheets with a domain size up to 4.5 nm, which was unobserved in the nanocrystalline cores of HD graphite grains. We also report on X-ray absorption near-edge structure measurements of G6. The complex isotopic- and micro-structure of G6 provides evidence for mixing and/or granular transport in SN ejecta.