Heterogeneous distribution of Al-26 at the birth of the Solar System

Abstract

It is believed that Al-26, a short-lived (t1/2 = 0.73 Ma) and now extinct radionuclide, was uniformly distributed in the nascent Solar System with the initial Al-26/Al-27 ratio of ~5.2\times10-5, suggesting its external stellar origin. However, the stellar source of Al-26 and the manner in which it was injected into the solar system remain controversial: the Al-26 could have been produced by an asymptotic giant branch star, a supernova, or a Wolf-Rayet star and injected either into the protosolar molecular cloud or protoplanetary disk. Corundum (Al2O3) is thermodynamically predicted to be the first condensate from a cooling gas of solar composition. Here we show that micron-sized corundum condensates from O-16-rich gas (Big Delta O-17 ~ -25%) of solar composition recorded heterogeneous distribution of Al-26 at the birth of the solar system: the inferred initial Al-26/Al-27 ratio ranges from ~6.5x10-5 to <2x10-6; ~50% of the corundum grains measured are Al-26-poor. Other Al-26-poor, O-16-rich refractory objects include grossite (CaAl4O7)- and hibonite(CaAl12O19)-rich calcium-aluminum-rich inclusions (CAIs) in CH chondrites, platy hibonite crystals in CM chondrites, and FUN (fractionation and unidentified nuclear isotopic anomalies) CAIs in CV, CO, and CR chondrites. Considering the apparently early and short duration (<0.3 Ma) of condensation of refractory O-16-rich solids in the solar system, we infer that Al-26 was injected into the collapsing protosolar molecular cloud and later homogenized in the protoplanetary disk. The apparent lack of correlation between Al-26 abundance and O-isotope compositions of corundum grains put important constraints on the stellar source of Al-26 in the solar system.

Astrophysical Journal Letters 733, L31

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Cited by in corpus (16)

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• Isotopic enrichment of forming planetary systems from supernova pollution
• Mixing of Clumpy Supernova Ejecta into Molecular Clouds
• Tracking the distribution of ${}^{26}$Al and ${}^{60}$Fe during the early phases of star and disk evolution
• Short-lived radioactivity in the early Solar System: the Super-AGB star hypothesis
• Aluminium-26 from massive binary stars II. Rotating single stars up to core-collapse and their impact on the early Solar System
• Intermediate-mass asymptotic giant branch stars and sources of ${}^{26}$Al, ${}^{60}$Fe, ${}^{107}$Pd, and ${}^{182}$Hf in the solar system
• Fingerprints of the protosolar cloud collapse in the Solar System I: Distribution of presolar short-lived ${}^{26}$Al
• Aluminium-26 from massive binary stars III. Binary stars up to core-collapse and their impact on the early Solar System
• Modification of the radioactive heat budget of Earth-like exoplanets by the loss of primordial atmospheres
• Refractory Metal Nuggets -- Formation of the First Condensates in the Solar Nebula
• Starbursts and High-Redshift Galaxies are Radioactive: High Abundances of ${}^{26}$Al and Other Short Lived Radionuclides
• Aluminium-26 production in low- and intermediate-mass binary systems