Bonanza: An extremely large dust grain from a supernova

1,2Frank Gyngard, 1Manavi Jadhav, 2Larry R. Nittler, 3Rhonda M. Stroud, 1Ernst Zinner
Geochimica et Cosmochimica Acta (in Press) Link to Article []
1Laboratory for Space Sciences and the Physics Department, Washington University, One Brookings Drive, St. Louis, MO 63130, USA
2Department of Terrestrial Magnetism, Carnegie Institution, Washington DC 20015, USA
3US Naval Research Laboratory, Code 6360, Washington DC 20375, USA
Copyright Elsevier

We report the morphology, microstructure, and isotopic composition of the largest SiC stardust grain known to have condensed from a supernova. The 25-μm diameter grain, termed Bonanza, was found in an acid-resistant residue of the Murchison meteorite. Grains of such large size have neither been observed around supernovae nor predicted to form in stellar environments. The large size of Bonanza has allowed the measurement of the isotopic composition of more elements in it than any other previous presolar grain, including: Li, B, C, N, Mg, Al, Si, S, Ca, Ti, Fe, and Ni. Bonanza exhibits large isotopic anomalies in the elements C, N, Mg, Si, Ca, Ti, Fe, and Ni typical of an astrophysical origin in ejecta of a Type II core-collapse supernova and comparable to those previously observed for other presolar SiC grains of type X. Additionally, we extracted multiple focused ion beam lift-out sections from different regions of the grain. Our transmission electron microscopy demonstrates that the crystalline order varies at the micrometer scale, and includes rare, higher order polytype domains (e.g., 15R). Analyses with STEM-EDS show Bonanza contains a heterogeneous distribution of subgrains with sizes ranging from < 10 nm to >100 nm of Ti(N,C); Fe, Ni-rich grains with variable Fe:Ni; and (Al,Mg)N. Bonanza also has the highest ever inferred initial 26Al/27Al ratio, consistent with its supernova origin. This unique grain affords us the largest expanse of data, both microstructurally and isotopically, to compare with detailed calculations of nucleosynthesis and dust condensation in supernovae.


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