Triggered Star Formation Inside the Shell of a Wolf-Rayet Bubble as the origin of the Solar System

Vikram V. Dwarkadas (University of Chicago), Nicolas Dauphas (University of Chicago), Bradley Meyer (Clemson University), Peter Boyajian (University of Chicago), Michael Bojazi (Clemson University)
(Submitted on 28 Dec 2017)

A critical constraint on solar system formation is the high $^{26}$Al/$^{27}$Al abundance ratio of 5 $\times 10^{-5}$ at the time of formation, which was about 17 times higher than the average Galactic ratio, while the $^{60}$Fe/$^{56}$Fe value was about $2 \times 10^{-8}$, lower than the Galactic value. This challenges the assumption that a nearby supernova was responsible for the injection of these short-lived radionuclides into the early solar system. We show that this conundrum can be resolved if the Solar System was formed by triggered star formation at the edge of a Wolf-Rayet (W-R) bubble. Aluminium-26 is produced during the evolution of the massive star, released in the wind during the W-R phase, and condenses into dust grains that are seen around W-R stars. The dust grains survive passage through the reverse shock and the low density shocked wind, reach the dense shell swept-up by the bubble, detach from the decelerated wind and are injected into the shell. Some portions of this shell subsequently collapses to form the dense cores that give rise to solar-type systems. The subsequent aspherical supernova does not inject appreciable amounts of $^{60}$Fe into the proto-solar-system, thus accounting for the observed low abundance of $^{60}$Fe. We discuss the details of various processes within the model and conclude that it is a viable model that can explain the initial abundances of $^{26}$Al and $^{60}$Fe. We estimate that 1-16% of all Sun-like stars could have formed in such a setting of triggered star formation in the shell of a WR bubble.

Comments:    19 pages, 6 figures. Accepted version. Final published version with proof corrections can be found on the Astrophysical

Journal web page for ApJ, 2017, 851, 147
Subjects:    Solar and Stellar Astrophysics (astro-ph.SR)
Journal reference:    Astrophysical Journal, 2017, Vol 851, 147
Cite as:    arXiv:1712.10053 [astro-ph.SR] (or arXiv:1712.10053v1 [astro-ph.SR] for this version)
Submission history
From: Vikram Dwarkadas
[v1] Thu, 28 Dec 2017 20:53:28 GMT (1566kb)
https://arxiv.org/abs/1712.10053