Unlayered graphenes in red-giant starsmoke

TL;DR

This paper presents evidence for unlayered graphene sheets in interstellar graphite onions, suggesting their formation in star atmospheres and proposing nucleation mechanisms based on structural and isotopic data.

Contribution

It provides the first structural evidence of unlayered graphene in space materials and discusses potential formation processes in stellar environments.

Findings

Detection of unlayered graphene sheets in meteorite samples

Structural analysis supports nucleation from pentagons in star atmospheres

Implications for carbon formation in late-stage star evolution

Abstract

Electron diffraction, imaging, and energy loss provide evidence for unlayered graphene sheets in the core of certain interstellar graphite onions (from the meteorite Murchison) whose isotopes indicate formation in the atmosphere of late-stage asymptotic giant branch stars (like those which nucleo-synthesized much of the earth's carbon). The data are compared to structural models loosely associated with atom-by-atom, molecule-by-molecule, and dendritic-droplet solidification processes. In this context the observed density, diffraction peak-shapes, and edge-on sheet patterns, along with theoretical limits on time for growth in the presence of outgoing radiation pressure, suggest nucleation of hexagonal sheets from pentagons, perhaps from a supercooled melt. These results warrant a closer examination of specimen structure, the energetics of unlayered graphene nucleation, and processes such as jets in late star atmospheres.