宇宙で重水素化メタノールを初めて検出（First detection of heavy methanol in space）

2026-10-07 マックス・プランク研究所

The Perseus molecular cloud is located about 1,000 light-years from Earth. A rare form of the organic alcohol methanol is present around at least one of the very young stars still embedded within it. The molecule has been detected in space for the first time ever in the current study. © Ekaterina Moerova / MPIfR; Background: NASA, CXC, SSC, NOAO, DSS; 3D image of methanol: https://pubchem.ncbi.nlm.nih.gov/compound/Methanol#section=3D-Conformer

＜関連情報＞

• https://www.mpg.de/26834976/first-detection-of-heavy-methanol-in-space
• https://www.aanda.org/articles/aa/full_html/2026/10/aa59642-26/aa59642-26.html

アルマ分光観測による原始星中の複雑な有機分子の探査（COMPASS） VII．星間空間における完全重水素化メタノールの初検出 Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VII. First interstellar detection of fully deuterated methanol

A. Belloche, S. Spezzano, A. Coutens, M. N. Drozdovskaya, J. K. Jørgensen, J.-E. Lee, A. L. Plunkett, D. Harsono, S. Maret, F. Cruz-Sáenz de Miera, J.-H. Jeong, P. Nazari, Y.-L. Yang, H.-S. Yun and S. Zeng
Astronomy & Astrophysics  Published:07 October 2026
DOI:https://doi.org/10.1051/0004-6361/202659642

Abstract

Context. There have been no robust identifications of fully deuterated methanol, CD₃OD, in the interstellar medium (ISM) to date.

Aims. Our goal is to continue the search for CD₃OD in star-forming regions to determine the deuteration pattern of methanol and set constraints on the deuteration process.

Methods. We used a sensitive imaging spectral survey of the protostellar system IRAS4A in the NGC1333 molecular cloud performed as part of the large program carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) called Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS). The column densities of methanol and several of its less abundant isotopologs, including deuterated ones, were derived under the assumption of local thermodynamic equilibrium (LTE).

Results. Along with the detection of several methanol isotopologs toward the binary component IRAS4A2, we report the first interstellar detection of CD₃OD. The deuteration pattern of methanol in IRAS4A2 is similar to the pattern measured in other low-mass protostars, with an increase in the apparent D/H ratio from the singly to multiply deuterated isotopologs. Chemical models of prestellar and protostellar cores focused on deuteration do not reproduce this pattern quantitatively. This discrepancy is even more exacerbated by the detection of CD₃OD. Our LTE modeling of the spectra yields low column density ratios of methanol to its ¹³C and ¹⁸O isotopologs while the ¹³C to ¹⁸O and ¹⁸O to ¹⁷O ratios are consistent with the isotopic ratios expected in the local ISM. We suspect that the column density of methanol is underestimated. One possible explanation is that the emission is clumpy rather than monolithic.

Conclusions. The first detection of a fully deuterated COM highlights the power of deuterium fractionation as a diagnostic tool for investigating the formation and inheritance of organic molecules during the process of star formation.