Triggered Star Formation inside the Shell of a Wolf–Rayet Bubble as the Origin of the Solar SystemOPEN ACCESS 

Vikram V. Dwarkadas, Nicolas Dauphas, Bradley Meyer, Peter Boyajian, and Michael Bojazi

The Astrophysical Journal, Volume 851, Number 2


“A critical constraint on solar system formation is the high 26Al/27Al abundance ratio of 5×10-5 at the time of formation, which was about 17 times higher than the average Galactic ratio, while the 60Fe/56Fe value was about 2×10-8 lower than the Galactic value. This challenges the assumption that a nearby supernova (SN) 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 a triggered star formation at the edge of a Wolf–Rayet (W–R) bubble. 26Al 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 collapse to form the dense cores that give rise to solar-type systems. The subsequent aspherical SN does not inject appreciable amounts of 60Fe into the proto–solar system, thus accounting for the observed low abundance of 60Fe. 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 26Al and 60Fe. 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 W–R bubble.”