The Rigakubu News

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Making Organic Dust in the Universe

Tatsuki Sakon (Assistant Professor, Department of Astronomy)

Izumi Endo (2nd Year Doctoral Student, Department of Astronomy)

Old stars emit stellar wind containing heavy elements into interstellar space, which is the site of formation of "organic dust. Novas are one such example, and the gas ejected by novas can contain nitrogen at concentrations several hundred times higher than that of the solar wind. The proportion of material originating from novae is not large in the total interstellar material. However, several novae have been observed to emit unidentified infrared bands, and novae are a valuable astronomical phenomenon for observing the nature of freshly formed organic dust.

Therefore, attempts have been made to simulate the synthesis of interstellar material on the ground and to reproduce the characteristics of the observed unidentified infrared bands. The microwave plasma generator used in this study was constructed by Research Associate Akira Sakata of the University of Electro-Communications in the late 1970s. In 2008, Associate Professor Setsuko Wada of the University of Electro-Communications retired from the University of Electro-Communications. Associate Professor Setsuko Wada of the University of Electro-Communications retired in 2008, the instrument was transferred to the Department of Astronomy at the University of Tokyo.

While quenched carbonaceous matter is organic dust composed of carbon and hydrogen, we have been working on the synthesis of nitrogen-containing organic dust. We found that the infrared absorption spectra of the organic dust obtained by quenching and condensing the plasma produced by microwave heating of a solid hydrocarbon sample and dilute nitrogen gas reproduce well the features of unidentified infrared bands observed in novae. X-ray absorption near-edge structure analysis revealed that the quenched nitrogen-included carbonaceous compacts contain nitrogen in the form of amines. The results of X-ray absorption near edge structure analysis revealed that the quenched nitrogen-included carbonaceous

Figure: (Left) Comparison of the IR absorbance spectrum of the quenched nitrogen-bearing carbonaceous material QNCC with an unidentified IR band observed in the nova V2361Cyg. (Right) Synthesis of quenched nitrogen-bearing carbonaceous matter.

The infrared properties of the quenched nitrogen-bearing carbonaceous material are similar to those of insoluble organic matter extracted from carbonaceous chondrite meteorites. As the origin of organic matter in the solar system, it is possible that organic dust produced by an old star survives after a long journey through the harsh interstellar space and is incorporated into the birthplace of a new solar system. Since 2015, we have been using ExHAM, a simple exposure experiment device on the Kibo module of the International Space Station, to investigate the degenerative process of organic dust by exposing laboratory-synthesized quenched nitrogen-containing carbonaceous matter to the space environment near the sun. We will compare the recovered samples with primitive organic matter of the solar system contained in meteorites and other materials actually collected from space to test the previous hypothesis.

We hope that the quenched nitrogen-containing carbonaceous material will help us to understand whether our existence in the solar system is commonplace in the long history of the universe by mobilizing both astronomical and geoscientific methods.

The results of this research have been published in I. Endo et al . , The Astrophysical Journal 917, 103 (2021).

(Press release, August 26, 2021)

Published in the January 2022 issue of Faculty of Science News

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