2023 Fiscal Year Final Research Report

Unraveling the origin and evolution of r-process elements based on the interpretation of elemental abundances measured for stars and meteorites

Research Project

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Project/Area Number	18H01258
Research Category	Grant-in-Aid for Scientific Research (B)
Allocation Type	Single-year Grants
Section	一般
Review Section	Basic Section 16010:Astronomy-related
Research Institution	National Astronomical Observatory of Japan
Principal Investigator	Tsujimoto Takuji 国立天文台, JASMINEプロジェクト, 助教 (10270456)
Co-Investigator(Kenkyū-buntansha)	横山哲也東京工業大学, 理学院, 教授 (00467028)
Project Period (FY)	2018-04-01 – 2023-03-31
Keywords	r過程元素 / 中性子星合体 / ブラックホール / 重力崩壊型超新星 / 隕石 / 同位体比異常
Outline of Final Research Achievements	The astrophysical origin of elements such as gold and platinum formed through rapid neutron-capture process, the so-called r-process, has been identified to be binary neutron star mergers through the detection of gravitational wave from the corresponding object in 2017 summer. Since this discovery, we have entered the era when the verification of neutron star mergers as the site of r-process is strongly desired. In this study, we have assessed this issue from the unique approaches using stellar abundances, the models for Galactic chemical evolution, and meteorite analysis. We eventually got to the conclusion that stellar abundances in the Galaxy are compatible with the hypothesis that rare core-collapse supernovae together with neutron star mergers are the origin of r-process elements. In addition, we find that the ejection of r-process elements from neutron star-black hole binaries is the another key factor for understanding the r-process evolution in the early Galaxy.
Free Research Field	理論宇宙物理
Academic Significance and Societal Importance of the Research Achievements	本研究成果は一般にも馴染みのある金やプラチナに代表される貴金属、レアアースといった元素の起源に関して新たな知見を与えるものである。地球で希少価値のあるこれらの元素が、宇宙において如何に稀な天体現象で作り出されてきたかを検証した結果、中性子星という究極の状態にある星同士が合体するという現象と非常に稀な種類の超新星爆発で生まれるという理論仮設を銀河化学進化の独自の視点から実証した。さらに、より稀な現象である中性子星とブラックホールの連星合体が貴金属を作る重要なサイトであることを明らかにし、ブラックホールと金との意外な関連性をも提示でき、社会的インパクトも大きい成果と言える。