7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Understanding of the properties of cosmic organic dust
based on combined approaches among astronomical observations,experiments and numerical simulations
Itsuki Sakon1, Takashi Onaka1, Takashi Miyata1, Kensei Kobayashi2, Yoko Kebukawa2, Junichi
Takahashi2, Masahiro Kobayashi3, Hiroaki Nakamura3, Mamoru Shoji3, Suguru Masuzaki3,
Masahiro Tanaka3
1
Graduate School of Science, University of Tokyo, 2 National Institute for Fusion Sciences,National Institutes of Natural Sciences, 3 Faculty of Engineering, Yokohama National University
e-mail (speaker): isakon@astron.s.u-tokyo.ac.jp
responsible for these bands and the determination of thephysical factors giving rise to their characteristics remainunresolved for galaxies with weak active galactic nuclei
and elliptical galaxies. In this presentation, I will report
the latest progress in research aimed at understanding theproperties of interstellar organic matter, based on an
integrated approach involving astronomical observations,experimental astrophysics, and molecular dynamics
simulations.
References[1] J. D. Bregman et al. 2008, ASP Conf. Ser. 381, 34[2] I. Endo, I. Sakon, T. Onaka et al. 2021, ApJ, 917, 103[3] H. Kaneda et al. 2005, ApJ, 632, 83[4] J. D. T. Smith et al. 2007, ApJ, 656, 770
0.1

ﬁlmy QCC (raw material)

absorbance (arbitral unit)

0.09

processed with Nitrogen plasma

0.08

generated by 2.45GHz microwave discharge

0.07
0.06
0.05
0.04
0.03
0.02
0.01
00.1

56

7

8910111213

1415

12131415

ﬁlmy QCC (raw material)

0.09

absorbance (arbitral unit)

At least a part of the Organic dust in space is believed
to be formed by condensing the stellar wind containing
nucleo-synthesized heavy elements. So far, experiments
have been conducted to synthesize materials simulating
the organic dust in space by generating plasma gas usinghydrocarbon dust and nitrogen gas with a 2.45 GHz
microwave and rapidly cooling and condensing it. Theseexperiments successfully synthesized Quenched
Nitrogen-included carbonaceous composite (QNCC) that
replicate the characteristics of unidentified infrared
bands observed around novae (Endo et al. 2021; see
upper panel of the Figure). This experiment qualitatively
simulates the process of organic dust formation in novae
where the N-rich nova wind interact with the pre-existinghydrocarbon dust. Analysis results reveal that QNCC
contains about 3-5% N/C ratio and contains nitrogen in
the form of amines within the material (Endo et al.
2021). Additionally, the infrared and X-ray analysis ofQNCC material collected after one year of exposure inorbit using the ExHAM facility on the InternationalSpace Station (ISS) ‘Kibo’ module showed striking
similarities to the insoluble organic matter (IOM) in
carbonaceous meteorites (Sakon et al. in preparation),suggesting QNCC's importance in investigating theorigin of primordial organic matter in the solar system.
On the other hand, with support from the program"Understanding the Process of Nitrogen-Inclusive
Chemical Bond Formation in Cosmic Organic Dust" (PI.
Itsuki Sakon) selected as part of the 2022 NINS CrossDisciplinary Joint Research Project, an experiment wasconducted at the Large Helical Device (LHD) of theNational Institute for Fusion Science, irradiatinghydrocarbon dust with a relatively low-energy plasma atthe outer edge of the LHD plasma (Cycle 24experiment). Preliminary analysis revealed changes that
reproduce the characteristics of peculiar unidentified
infrared bands observed in galaxies with weak active
galactic nuclei (Smith et al. 2007) and in ellipticalgalaxies (Bregman et al. 2008; Kaneda et al. 2005),
characterized by the absence of the 6-9μm bands
corresponding to stretching modes of aromatic C-C
bonds and the presence of only the 11-14μm bands
corresponding to out-of-plane bending modes ofaromatic C-H bonds (see bottom panel of Figure). While
the polycyclic aromatic hydrocarbons (PAHs) hypothesis
is widely accepted in astronomy as the carrier of thesebands, the exact understanding of their nature isincomplete. Thus, the identification of the carrier

processed with HLD plasma

0.08(Hydrogen, Nitrogen)

0.07
0.06
0.05
0.04
0.03
0.02
0.01
05678

91011wavelength (um)Figure 1. (top) Infrared ATR spectrum of organic dust
named QNCC (Endo et al. 2021) synthesized byirradiating nitrogen plasma generated by 2.45 GHz
microwave discharge to filmy QCC. (bottom) Infrared
ATR spectrum of organic dust synthesized by irradiating
LHD plasma made of hydrogen and Nitrogen to filmy
QCC. The infrared ATR spectrum of unprocessed filmy
QCC is shown with gray in both panel.