The Bubble-like Interior of the Core-Collapse Supernova Remnant Cassiopeia A

TL;DR

This study reveals a bubble-like interior structure in the Cassiopeia A supernova remnant, suggesting turbulent mixing and radioactive ejecta distribution as key to understanding core-collapse supernova asymmetries.

Contribution

It provides the first three-dimensional map of unshocked ejecta in Cassiopeia A, linking interior morphology to explosion dynamics and mixing processes.

Findings

Interior has a bubble-like morphology connected to multi-ringed structures.

Radioactive 56Ni-rich ejecta likely formed outwardly expanding plumes.

Substantial 56Fe may still reside in interior cavities.

Abstract

The death of massive stars is believed to involve aspheric explosions initiated by the collapse of an iron core. The specifics of how these catastrophic explosions proceed remain uncertain due, in part, to limited observational constraints on various processes that can introduce asymmetries deep inside the star. Here we present near-infrared observations of the young Milky Way supernova remnant Cassiopeia A, descendant of a type IIb core-collapse explosion, and a three-dimensional map of its interior, unshocked ejecta. The remnant's interior has a bubble-like morphology that smoothly connects to and helps explain the multi-ringed structures seen in the remnant's bright reverse shocked main shell of expanding debris. This internal structure may have originated from turbulent mixing processes that encouraged the development of outwardly expanding plumes of radioactive 56Ni-rich ejecta. If this is true, substantial amounts of its decay product, 56Fe, may still reside in these interior cavities.