PSR Discoveries

false-color SIMS image of presolar SiC grains

Once presolar grains have been concentrated by dissolving 99.9% of a meteorite, they can be studied in detail using electron microscopes and secondary ion mass spectrometers (also known as ion microprobes). Ion microprobes allow determination of not only elemental abundances, but isotopes as well. The abundances of isotopes can even be imaged, as shown in these photographs from Larry Nittler (Carnegie Institution). The colors are false, but are scaled to the abundances of silicon isotopes. Grains with 30Si/28Si typical of mainstream presolar SiC grains (see graph in main text) appear similar in both images. The grain indicated by an arrow is clearly deficient in 30Si and belongs to the rare subclass of presolar SiC known as X-grains. Whereas most SiC grains originated around low-mass, carbon-rich red giant stars, X-grains are thought to have condensed in supernova explosions.