The Remarkable Deaths of 9 - 11 Solar Mass Stars

TL;DR

This paper investigates the complex evolution and explosive deaths of 9-11 solar mass stars, revealing unique phenomena like off-center ignition, silicon flashes, and potential observable supernova signatures.

Contribution

It introduces a detailed stellar evolution model with reaction networks and sub grid convection modeling for stars in the 7-11 solar mass range, highlighting new explosive behaviors.

Findings

Stars between 9-10 solar masses experience off-center oxygen ignition.

Silicon flashes can cause early envelope ejection and multiple supernova-like events.

Potential observable signatures include faint silicon flashes and bright subsequent supernovae.

Abstract

The post-helium burning evolution of stars from 7 to 11 solar masses is complicated by the lingering effects of degeneracy and off-center ignition. Here stars in this mass range are studied using a standard set of stellar physics. Two important aspects of the study are the direct coupling of a reaction network of roughly 220 nuclei to the structure calculation at all stages and the use of a sub grid model to describe the convective bounded flame that develops during neon and oxygen burning. Below 9.0 solar masses, degenerate oxygen-neon cores form that may become either white dwarfs or electron-capture supernovae. Above 10.3 solar masses the evolution proceeds "normally" to iron-core collapse, without composition inversions or degenerate flashes. Emphasis here is upon the stars in between which typically ignite oxygen burning off center. After oxygen burns in a convectively bounded flame, silicon burning ignites in a degenerate flash that commences closer to the stellar center and with increasing violence for stars of larger mass. In some cases the silicon flash is so violent that it could lead to the early ejection of the hydrogen envelope. This might have interesting observable consequences. For example, the death of a 10.0 solar mass star could produce two supernova-like displays, a faint low energy event due to the silicon flash, and an unusually bright supernova many months later as the low energy ejecta from core collapse collides with the previously ejected envelope. The potential relation to the Crab supernova is discussed.