M. Audard, Hisamitsu Awaki, Ralf Ballhausen, Aya Bamba, Ehud Behar, Rozenn Boissay-Malaquin, Laura Brenneman, G. V. Brown, Lía Corrales, E. Costantini, Renata Cumbee, María Díaz Trigo, Chris Done, Tadayasu Dotani, Ken Ebisawa, Megan E. Eckart, D. Eckert, Teruaki Enoto, S. Eguchi, Yuichiro Ezoe, Adam Foster, Ryuichi Fujimoto, Yutaka Fujita, Yasushi Fukazawa, Kotaro Fukushima, Akihiro Furuzawa, Luigi Gallo, Javier A. García, Liyi Gu, M. Guainazzi, Kouichi Hagino, Kenji Hamaguchi, Isamu Hatsukade, Katsuhiro Hayashi, Takayuki Hayashi, Natalie Hell, Edmund Hodges‐Kluck, A. E. Hornschemeier, Yuto Ichinohe, Daiki Ishi, Manabu Ishida, Kumi Ishikawa, Yoshitaka Ishisaki, J. S. Kaastra, T. R. Kallman, Erin Kara, Satoru Katsuda, Yoshiaki Kanemaru, Richard L. Kelley, Caroline A. Kilbourne, Shunji Kitamoto, Shogo Kobayashi, Takayoshi Kohmura, Aya Kubota, Maurice A. Leutenegger, Michael Loewenstein, Yoshitomo Maeda, Maxim Markevitch, Hironori Matsumoto, Kyoko Matsushita, D. McCammon, B. R. McNamara, François Mernier, Eric D. Miller, J. M. Mïller, Ikuyuki Mitsuishi, Misaki Mizumoto, Tsunefumi Mizuno, Koji Mori, K. Mukai, Hiroshi Murakami, R. F. Mushotzky, Hiroshi Nakajima, Kazuhiro Nakazawa, Jan‐Uwe Ness, Kumiko Nobukawa, Masayoshi Nobukawa, Hirofumi Noda, Hirokazu Odaka, Shoji Ogawa, Anna Ogorzałek, Takashi Okajima, Naomi Ota, S. Paltani, Robert Petre, Paul P. Plucinsky, F. S. Porter, K. Pottschmidt, Kosuke Sato, Toshiki Sato, Makoto Sawada, Hiromi Seta, M. Shidatsu, A. Simionescu, Randall K. Smith, Hiromasa Suzuki, Andrew E. Szymkowiak, H. Takahashi, Mai Takeo, Toru Tamagawa
The elements in the Universe are synthesized primarily in stars and supernovae, where nuclear fusion favours the production of even-Z elements. In contrast, odd-Z elements are less abundant and their yields are highly dependent on detailed stellar physics, making theoretical predictions of their cosmic abundance uncertain. In particular, the origin of odd-Z elements such as phosphorus (P), chlorine (Cl) and potassium (K), which are important for planet formation and life, is poorly understood. While the abundances of these elements in Milky Way stars are close to solar values, supernova explosion models systematically underestimate their production by up to an order of magnitude, indicating that key mechanisms for odd-Z nucleosynthesis are currently missing from theoretical models. Here we report the observation of P, Cl and K in the Cassiopeia A supernova remnant using high-resolution X-ray spectroscopy with X-Ray Imaging and Spectroscopy Mission data, with the detection of K at above the 6σ level being the most significant finding. Supernova explosion models of normal massive stars cannot explain the element abundance pattern, especially the high abundances of Cl and K, while models that include stellar rotation, binary interactions or shell mergers agree closely with the observations. Our observations suggest that such stellar activity plays an important role in supplying these elements to the Universe. XRISM observations show the presence of odd-numbered elements chlorine and potassium in Cas A. These findings suggest that stellar activity plays an important role in cosmic chemical evolution, enriching space with elements vital for planets and life.