Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21530108k&link_type=abstract
American Astronomical Society, AAS Meeting #215, #301.08; Bulletin of the American Astronomical Society, Vol. 42, p.298
Astronomy and Astrophysics
Astronomy
Scientific paper
Evolved stars supply first organic materials into space. The organic materials evolve and alter to form more complex organic molecules before incorporation into the star formation stage. Polycyclic aromatic hydrocarbons (PAH) are most plausible molecules abundantly produced within the gas ejected from evolved stars. A single aromatic ring, benzene, can be made from acetylene molecules (Woods et al. 2002; Woods et al. 2003). Benzene grows to larger PAHs by the abstraction of ring hydrogen and further interaction with acetylene (Bittner & Howard 1981; Frenklach et al. 1984). During the growth of PAH molecules, and as they move away from the central star, larger PAHs coagulate to form PAH grains (Rapacioli et al. 2005). The progression of organic materials after PAH grains has been unknown. We performed simulation experiments to find their evolutional process after PAH grains and demonstrate the possible formation site, process, and starting material.
Condensation experiments are involved exposing a vapor phase to plasma to form carbonaceous grains, a situation that exists ubiquitously in space. Benzene was introduced into the He plasma. After the experiment, brown- to yellowish-colored materials were obtained by the decomposition of benzene due to polymerization. After transmission electron microscope observation, we found formation of organic grains with cavity in their center. The hollow interior could be formed by coagulation of atomic vacancies, produced by electronic excitation and/or knock-out of carbon atoms following irradiation by plasma particles. Similar extraterrestrial organic grains, called organic globules, have been found abundantly in several carbonaceous chondrites, which often have a cavity in their center (Nakamura-Messenger et al. 2006).
The result suggests that organic globules are possibly the final products in the evolution of carbonaceous matter from acetylene, benzene to PAH in ejecta gas from evolved stars, i.e., abundant PAH molecules around evolved stars may connect to the organic globules.
Kimura Yuki
Saito Masao
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