Physical origin of the present-day compositional asymmetry

Determine whether the large-scale segregation between Ne-rich and Si-enhanced O-rich ejecta in Cassiopeia A primarily reflects spatially heterogeneous presupernova shell-merger burning, asymmetric ejecta transport during the explosion, or subsequent remnant evolution.

Background

The study finds that Ne-rich ejecta are concentrated preferentially toward the north and northeast, whereas Si-enhanced O-rich ejecta are more prominent in the southeast. Comparisons with one-dimensional presupernova models suggest distinct degrees of O-shell processing, but the current observations cannot uniquely determine whether the observed spatial arrangement was established before collapse or substantially modified during and after the explosion.

The authors propose a physically motivated scenario involving direction-dependent fuel entrainment and convective-reactive burning followed by asymmetric transport associated with Fe-rich plumes, while explicitly acknowledging that the scenario is not unique. Higher-resolution soft-X-ray observations are identified as necessary to distinguish among the competing origins.