[meteorite-list] NRL and Carnegie Institution Scientists Examine the Life Cycle Of Stars Encoded In Tiny Grains Of Dust

[Ron Baalke]

Public Affairs Office
Naval Research Laboratory
Washington, D.C.

9/2/2004

Press Release 45-04r

NRL and Carnegie Institution Scientists Examine the Life Cycle Of Stars Encoded 
In Tiny Grains Of Dust

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.

IMAGE CAPTION:
[http://www.nrl.navy.mil/pao/PressReleases/2004/45-presolargrain.jpg (37KB)]
This scanning electron microscope image shows one of the aluminum oxide stardust 
grains studied by the NRL/Carnegie Institution research team.