Event Overview
- Subject: Galactic Chemical Evolution
- Lecturer: Prof. Chiaki Kobayashi (University of Hertfordshire)
- Date: 29-30 Oct. 2026
- Venue: Mitaka Campus NAOJ (National Astronomical Observatory of Japan)
- Expected Audience: PhD students, early-career researchers, and non-specialist researchers interested in stellar nucleosynthesis and galactic evolution
Abstract
During the Big Bang, only light elements such as hydrogen and helium were produced. Carbon and heavier elements (called metals in astronomy) are created inside stars and are ejected when they die. Iron-peak and neutron-capture elements are further produced by binaries - Type Ia supernovae and neutron star mergers, respectively. These elements are distributed into the interstellar medium, and new stars formed from this gas contain elements produced by previous generations of stars. Therefore, stars are fossils that retain the history of their host galaxy. Detailed elemental abundances of individual stars in the Milky Way have been extremely useful for constraining stellar nucleosynthesis and the origin of elements. Not only metallicities but also elemental abundance ratios evolve in galaxies, which can be used to constrain stellar astrophysics and galaxy evolution.
In our zoom-in simulation of a Milky Way type galaxy, the basic structures of the Galaxy and their stellar populations are reproduced very well; the bulge formed by the assembly of small gas-rich galaxies at high-redshifts has old and high-alpha stellar populations, while the disk formed inside-out with a longer timescale has younger and lower-alpha stellar populations due to the delayed enrichment from Type Ia supernovae, which results in the bimodal distribution of the alpha-to-iron ratios observed in the Milky Way Galaxy and M31 Andromeda Galaxy. For the elements heavier than iron, it is not possible to reproduce observations with neutron star mergers only and the contributions from magneto-rotational supernovae is required.
In large-scale cosmological simulations, including feedback from active galactic nuclei that originate the first stars, chemical and dynamical properties of various types of galaxies are fairly well reproduced. Metallicity is higher in more massive galaxies (leading to the mass-metallicity relation), and at the centre of galaxies (causing metallicity radial gradients), broadly following elemental abundance trends expected by nuclear astrophysics. With the James Webb Space Telescope, unexpected elemental-abundance ratios (namely high N/O) are detected for very high redshift star-forming galaxies, which can be explained with Wolf-Rayet stars under intermittent star formation. Comparing various elemental abundances (CNO, Ne, and Ar) to the galactic chemical evolution models, it will be possible to confirm the dominant enrichment source as well as constraining galaxy formation processes across Cosmic Time.
Lecturer
Prof. Chiaki Kobayashi
Professor at the University of Hertfordshire. She received her B.Sc. in Astronomy from the Faculty of Science at the University of Tokyo and completed his Ph.D. in Astronomy at the University of Tokyo, earning a Doctor of Science degree. After research appointments at the Max Planck Institute for Astrophysics and Australian National University, he joined the University of Hertfordshire, where he currently serves as Professor.
Her research focuses on the formation and evolution of galaxies and the origin of the chemical elements in the Universe, using large-scale supercomputer simulations. She is a co-author of the book How Were the Elements Made? — Supernova Explosions and the Chemical Evolution of the Universe (Iwanami Lecture Series: The World of Physics). She is currently a Visiting Senior Scientist at the Kavli Institute for the Physics and Mathematics of the Universe. She also serves as the coordinator of BRIDGECE, the UK network for nuclear astrophysics. In 2024, she was awarded the George Darwin Lectureship by the Royal Astronomical Society.
This lecture will be followed by the OMEG18 conference at RIKEN (Oct. 20–23).
Organizers
- Wako Aoki (NAOJ)
- Hiroko Okada (NAOJ)
- Nobuya Nishimura (Kogakuin U)
- Shunji Nishimura (RIKEN)
Support
- Quantum Matter Science in the Universe Opened Up by Precise Numerical Calculations (QMS)
- National Astronomical Observatory of Japan (NAOJ)
- UKAKUREN ?
