2026-05-08 京都大学
超高エネルギー極重宇宙線原子核の模式図。中性子星連星合体や大質量星の崩壊で作られた極重原子核が加速され、宇宙背景光と相互作用しながら地球へ届く様子を示す。作成：B. T. Zhang and K. Murase（Google SlidesおよびそのAI支援機能を使用）
＜関連情報＞
- https://www.kyoto-u.ac.jp/ja/research-news/2026-05-08
- https://journals.aps.org/prl/abstract/10.1103/221m-gvs3
極重・超高エネルギー宇宙線 Ultraheavy Ultrahigh-Energy Cosmic Rays
B. Theodore Zhang, Kohta Murase, Nick Ekanger, Mukul Bhattacharya, and Shunsaku Horiuchi
Physical Review Letters Published: 7 May, 2026
DOI: https://doi.org/10.1103/221m-gvs3
Abstract
We investigate the propagation of ultraheavy (UH) nuclei as ultrahigh-energy cosmic rays (UHECRs). We show that their energy loss lengths at ≲300 EeV are significantly longer than those of protons and intermediate-mass nuclei, and that the highest-energy cosmic rays with energies beyond ∼100 EeV, including the Amaterasu particle, may be UH-UHECRs. For the first time, we derive constraints on the contribution of UH-UHECR sources, and find that the current data are consistent with energy generation rate densities of UHECRs from collapsars and neutron star mergers. Our model predicts that the mean value of the depth of shower maximum is lower than that for iron nuclei beyond 100 EeV, which can be tested with future composition measurements, e.g., AugerPrime and the Global Cosmic Ray Observatory. In addition, the spectral tension between the Telescope Array (TA) and the Pierre Auger Observatory can be alleviated by considering the enhanced contribution of UHECRs—including UH nuclei—from a nearby transient.
