Deciphering the Remnants of Core-Collapse Supernovae: Reconstructing Progenitor Star Properties and Explosion Mechanisms

TL;DR

This study uses advanced 3D simulations to connect supernova explosion physics and ejecta-CSM interactions with the complex observed structures of Cassiopeia A, revealing how initial explosion conditions and environmental effects shape remnant morphology.

Contribution

First detailed 3D hydrodynamic and magnetohydrodynamic simulations of Cas A from core collapse to 1000 years, incorporating key physical processes to explain observed ejecta structures.

Findings

Filamentary ejecta network forms during early explosion due to instabilities.

Green Monster morphology results from dense ejecta interacting with asymmetric CSM.

Radiative cooling enhances fragmentation, creating holes and rings.

Abstract

(Abridged) Recent JWST observations of Cassiopeia A (Cas A) reveal unprecedented ejecta substructure, including a web of filaments and the enigmatic "Green Monster" (GM), characterized by nearly circular holes and rings. These features provide new constraints on supernova (SN) explosion physics and ejecta-circumstellar medium (CSM) interactions. We present high-resolution three-dimensional hydrodynamic and magnetohydrodynamic simulations of a neutrino-driven SN explosion tailored to Cas A, following the system from core collapse to an age of $\sim 1000$ yr. The models include key physical processes such as hydrodynamic instabilities, Ni-bubble effects, radiative cooling, non-equilibrium ionization, and electron-ion temperature equilibration. Our results show that the filamentary ejecta network naturally forms during the early explosion due to the interaction of neutrino-driven bubbles and instabilities, retaining a memory of the initial conditions before being progressively modified by the reverse shock. The GM morphology is reproduced by the interaction of dense ejecta clumps with an asymmetric, forward-shocked CSM shell, with radiative cooling enhancing fragmentation and generating the observed holes and rings. Overall, our study demonstrates that Cas A's complex morphology reflects both the imprint of the explosion mechanism and subsequent ejecta-CSM interactions.