Observation of nucleosynthesis and circulation in the galaxy by nuclear gamma-ray imaging spectroscopy

2019 Fiscal Year Final Research Report

• Project/Area Number: 16H02185
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Particle/Nuclear/Cosmic ray/Astro physics
• Research Institution: Kyoto University
• Principal Investigator: Tanimori Toru 京都大学, 理学研究科, 教授 (10179856)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Keywords: MeVガンマ線物理学 / 原子核宇宙物理学 / ETCC / 銀河拡散ガンマ線 / 銀河中心 / 元素合成 / 暗黒物質 / 原始ブラックホール

Outline of Final Research Achievements

MeV gamma astronomy is the only window for the direct observation of nucleosynthesis. However, the study has been stagnated due to the incomplete imaging method and huge background. We developed an electron track detection Compton camera, succeeded in measuring the direction of arrival of a MeV gamma ray, and established a proper gamma ray imaging technology. Then we constructed SMILE2 + instrument that can detect both the gamma emissions of Galactic center 511 keV and Crab in one day. We observed the Galactic Center using JAXA Australian balloon in 2018. As planned, Crab and Galactic Center 511 keV were detected with 4-5σ. Furthermore, both the galactic diffuse and the cosmic diffuse gammas were detected with 10 sigma and more, and their spectra are being obtained. In particular, it is proved that the excess of gammas of Galactic diffuse was more an order of magnitude higher than the theory, which may suggest the existence of an unknown mechanism such as decay from dark matter.

Free Research Field

宇宙線物理学

Academic Significance and Societal Importance of the Research Achievements

MeVガンマ線は原子核反応で出る核ガンマ線であり、大きな謎である宇宙元素合成を直接観測出来る窓である。さらに物質状態での最高温度もMeVであり、宇宙の超高温状態、を調べる有力な手段である。また太陽や地球近傍での高エネルギー粒子もMeV領域であり地球磁場、気候にも大きな影響を与える。このように宇宙論から地球環境まで重要な情報を与える観測の窓であったが画像法が不確定で天文学の中で唯一20年停滞していた。我々は核ガンマ線の完全可視化に世界で初めて成功、その成果を天体観測に利用し一気に従来法の感度を2桁近く上回ることを実証した。核ガンマ線は医療など応用分野も大きく、今後幅広い応用が期待できる。