NRL and Carnegie Institution Scientists Examine the Life Cycle of Stars Encoded in Tiny Grains of Dust

9/2/2004 - 45-04r
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Scientists at the Naval Research Laboratory and the Carnegie Institution of Washington are studying microscopic aluminum oxide stardust grains that predate the Sun. The analysis of the grains gives unique insight into the processes by which old stars shed dust that then becomes the raw material for the birth of new stars.

Dr. Rhonda Stroud, a research physicist in NRL's Materials Science and Technology Division, explains that the research team is "reverse engineering stars," by analyzing the presolar dust grains. Dr. Larry Nittler and Dr. Conel Alexander, from the Carnegie Institution of Washington, perform measurements of the oxygen and magnesium isotopes in the dust grains. These measurements reveal what kind of star the dust came from. Armed with these results, Dr. Stroud extracts 100-nanometer thin sections from the dust grains using techniques usually applied to site-specific defect analysis in microchips. Then she analyzes the structure of the dust using a transmission electron microscope. Once the structure of the dust is known, it is possible to infer the environmental conditions of stellar outflows in which the dust formed.

The research team discovered that O-rich asymptotic giant branch (AGB) stars produce aluminum oxide in crystalline and amorphous forms. These findings are important for Department of Defense researchers interested in what kinds of materials form in extreme environments, and can survive long-term exposure to the harsh radiation environments of space.

The physical data from the grains is also useful to astrophysicists who have been debating for 30 years the sequence of dust formation, and how materials get recycled from stars and interstellar-space Now the astrophysicists can directly compare the data from the grains, to the predictions of the dust condensation models. The data provide strong support to models of AGB stars that predict that aluminum oxide phases are the first to condense. The observational astronomy community will also benefit from having definitive evidence for the existence of two forms of aluminum oxide. The interpretation of IR spectra from the dust clouds around O-rich AGB stars has provoked intense debate over what type of aluminum oxide, if any, exists in these clouds. The analysis of the NRL-Carnegie team bridges the information gap faced by astrophysicists and astronomers by providing complete chemical, isotopic, and structural profiles of individual dust grains.

This research is being funded by the Office of Naval Research and the National Aeronautics and Space Administration. The results of this research are published in the 9/3/04 issue of Science.

This scanning electron microscope image shows one of the aluminum oxide stardust grains studied by the NRL/Carnegie Institution research team.

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