Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd..11e...8d&link_type=abstract
Pre-Solar Grains as Astrophysical Tools, 26th meeting of the IAU, Joint Discussion 11, 21 August 2006, Prague, Czech Republic, J
Astronomy and Astrophysics
Astrophysics
Scientific paper
The solid material in interstellar space - interstellar dust -- is formed in a wide range of different environments. It is well known that these include outflows from cool stars, and ejecta from nova and supernovae. In addition to this "stardust" from stellar sources, solid material is also grown in the interstellar medium itself. The relative importance of different formation/ growth sites remains controversial, but estimates of grain lifetimes against destruction lead to the conclusion that most of the solid matter in the interstellar medium was grown in the interstellar medium, rather than in stellar outflows. The composition of interstellar grains must therefore depend on what materials can be grown from the gas phase under interstellar conditions. I will review the evidence pointing to growth of grain material in the interstellar medium. Elements such as Si, and Fe appear to be incorporated primarily into amorphous silicate material. At least some, perhaps most, of the carbonaceous material is aromatic. The story of how this material forms in the interstellar medium is very uncertain, but involves atoms and molecules impinging on the cold surfaces of dust grains, with the resulting material exposed to far-ultraviolet radiation and cosmic rays. In addition to growth by incorporation of single atoms or molecules, coagulation is likely to be important. Until the day arrives when there are representative samples of interstellar dust to study in the laboratory, we must study it remotely, by scattering and absorption of light (from infrared to X-rays), by emission of light, primarily in the infrared, and by using indirect evidence, such as depletion of certain elements and isotopes from the gas phase. For example, evidence now appears to show that interstellar grains in many regions are extremely deuterated. The life stories of interstellar grains are strongly constrained by the observed properties of the interstellar grain population.
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