Three outer jets in Cas A unveil the complex phenomena occurring in the interior of an exploding star. The paper: “Extreme anisotropies in deep layers of an exploding star: overabundance of Cr in the northeastern jet of Cassiopeia A” of V. Sapienza (INAF-OAPA/UNIPA) appeared on ApJL

In the supernova remnant Cassiopeia A, three jets rich in material synthesized in the innermost layers of the progenitor star reveal the secrets of the processes that occur in a supernova immediately after core collapse.

Understanding the phenomena that follow the collapse of a massive star core is one of the most important goals of modern astrophysics. These processes play a fundamental role in the distribution of chemically enriched material from the progenitor star into the Universe after the supernova explosion. However, this is a complex field of research, not only because of the rarity of core-collapse supernovae occurring close to Earth, but also because there are no diagnostic tools that allow us to directly observe the interiors of massive stars.

The study of supernova remnants can provide valuable clues, particularly through the analysis of morphological, dynamical, and chemical asymmetries in the ejected material. Some remnants, for example, show clear jets of material enriched with elements synthesized in the stellar interior. These collimated jets are thought to be generated and accelerated to high velocities as a consequence of complex physical processes in the deepest regions of the progenitor stars. Besides, since they move faster than the other stellar fragments expelled by the supernova (the ejecta), the jets carry elements produced in the innermost layers outward transporting them into the outer regions of the remnant.

The supernova remnant Cassiopeia A (Cas A), located about 11000 light years away and only 350 years old, is well known for its highly asymmetric structure and the presence of prominent jets. A team of researchers led by astrophysicist V. Sapienza (INAF – Astronomical Observatory of Palermo and University of Palermo) analyzed a long X-ray observation of Cas A, totaling nearly 280 hours, obtained with NASA Chandra satellite. The study focused on three jets visible in the northeastern section of the remnant. The analysis revealed high abundances of chromium, along with other elements such as argon, sulfur, and silicon.

Interpreted in the framework of models of the internal structure of massive stars, the results suggest that the three jets were expelled from very deep regions of the star, particularly from the layer where thermonuclear reactions consuming silicon were taking place, close to the core. The data further indicate that these layers underwent processes that caused a rapid mixing of the chemical elements synthesized in different stellar shells.

The study is described in the article “Extreme anisotropies in deep layers of an exploding star: overabundance of Cr in the northeastern jet of Cassiopeia A”, recently published in The Astrophysical Journal Letters. The article is co-authored by researchers E. Greco, S. Orlando, and F. Bocchino (INAF – Astronomical Observatory of Palermo) and M. Miceli (University of Palermo).

The cover image shows an X-ray picture of Cassiopeia A, highlighting the three jets analyzed in this study.