High-entropy ejecta plumes in Cassiopeia A from neutrino-driven convection

Toshiki Sato; Keiichi Maeda; Shigehiro Nagataki; Takashi Yoshida; Brian Grefenstette; Brian J Williams; Hideyuki Umeda; Masaomi Ono; John P Hughes

doi:10.1038/s41586-021-03391-9

High-entropy ejecta plumes in Cassiopeia A from neutrino-driven convection

Nature. 2021 Apr;592(7855):537-540. doi: 10.1038/s41586-021-03391-9. Epub 2021 Apr 21.

Authors

Toshiki Sato^{1

2

3

4}, Keiichi Maeda⁵, Shigehiro Nagataki^{6

7}, Takashi Yoshida^{8

9}, Brian Grefenstette¹⁰, Brian J Williams¹¹, Hideyuki Umeda⁸, Masaomi Ono^{6

7}, John P Hughes¹²

Affiliations

¹ RIKEN, Wako, Japan. [email protected].
² NASA, Goddard Space Flight Center, Greenbelt, MD, USA. [email protected].
³ Department of Physics, University of Maryland Baltimore County, Baltimore, MD, USA. [email protected].
⁴ Department of Physics, Rikkyo University, Tokyo, Japan. [email protected].
⁵ Department of Astronomy, Kyoto University, Kyoto, Japan.
⁶ Astrophysical Big Bang Laboratory (ABBL), RIKEN Cluster for Pioneering Research, Wako, Japan.
⁷ RIKEN Interdisciplinary Theoretical and Mathematical Science Program (iTHEMS), Wako, Japan.
⁸ Department of Astronomy, Graduate School of Science, University of Tokyo, Tokyo, Japan.
⁹ Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto, Japan.
¹⁰ Cahill Center for Astrophysics, California Institute of Technology, Pasadena, CA, USA.
¹¹ NASA, Goddard Space Flight Center, Greenbelt, MD, USA.
¹² Department of Physics and Astronomy, Rutgers University, Piscataway, NJ, USA.

PMID: 33883732
DOI: 10.1038/s41586-021-03391-9

Abstract

Recent multi-dimensional simulations suggest that high-entropy buoyant plumes help massive stars to explode^1,2. Outwardly protruding iron (Fe)-rich fingers of gas in the galactic supernova remnant^3,4 Cassiopeia A seem to match this picture. Detecting the signatures of specific elements synthesized in the high-entropy nuclear burning regime (that is, α-rich freeze out) would constitute strong substantiating evidence. Here we report observations of such elements-stable titanium (Ti) and chromium (Cr)-at a confidence level greater than 5 standard deviations in the shocked high-velocity Fe-rich ejecta of Cassiopeia A. We found that the observed Ti/Fe and Cr/Fe mass ratios require α-rich freeze out, providing evidence of the existence of the high-entropy ejecta plumes that boosted the shock wave at explosion. The metal composition of the plumes agrees well with predictions for strongly neutrino-processed proton-rich ejecta^2,5,6. These results support the operation of the convective supernova engine via neutrino heating in the supernova that produced Cassiopeia A.