Researchers at the McDonnell Center for the Space Sciences at Washington University recently identified two important stellar sources of the grains, or "stardust." Ernst Zinner, Ph.D., research professor in the departments of Physics and Earth and Planetary Sciences and in the McDonnell Center, all in Arts and Sciences, reported on the latest findings in the Jan. 5 issue of Science.
In his article, titled "Stardust in the Laboratory," Zinner writes that he and other researchers isolated and studied in the laboratory individual stellar dust grains that were discovered in meteorites. By measuring the isotopic composition of these grains using an ion microprobe, the researchers determined that the grains came from red giant stars of low to medium mass during late stages of their evolution and from supernovae, massive stars that exploded at the end of their evolution.
These grains, Zinner explained, condensed when the envelope of red giants cooled during expansion or when supernovae exploded, thus preserving the elemental and isotopic composition of their stellar sources. The red stars and supernovae each carry signature isotopic compositions that helped determine the grains' sources. Zinner, who is director of the McDonnell Center's Ion Microprobe Laboratory, said the ion probe data provide important information not available by astronomical observations.
"Finding that supernovae make grains in the first place has been exciting," said Zinner. "An added key finding is that our data on supernovae grains give convincing evidence that violent mixing of the ejecta took place during supernovae explosions. The isotopic compositions of these grains are providing us with information that cannot be attained in any other way."
In the last eight years, Zinner and his Washington University colleagues have identified three types of interstellar grains: silicon carbide, titanium carbide and graphite. Other types of grains recently found include aluminum oxide and silicon nitride. By studying the isotopic compositions of these grains, researchers gain information on nucleosynthesis -- the formation of the elements -- in stars as well as on processes in interstellar space and the early solar system.
-- Susan Killenberg
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