第172回 第2部

Galactic chemical evolution studies the enrichment histories of elements in the Universe. At the time of the Big Bang, the Universe consists of hydrogen, helium, and lithium. However, we are now living in the Universe with various kinds of elements. Most of the elements are synthesized in stars and distributed to space when a star ends its life.
These elements are inherited to the next generation stars. Elemental abundances of stars, therefore, reflect the nucleosynthetic histories in the galaxy. In the first part of this talk, I will show how the observed elemental abundances of stars in the Milky Way and satellite dwarf galaxies preserve information about their enrichment histories. In the Milky Way, the distribution of elements is different among old and new stars. The second part of this presentation focuses on the modeling of galaxy evolution. Hydrodynamic simulations of galaxies are presently a powerful tool to study galactic chemical evolution. It can self-consistently follow the formation of galaxies and the enrichment histories of elements. The last part discusses the enrichment of elements heavier than iron. The origin of elements synthesized by a rapid neutron-capture process such as europium, platinum, and gold is a long-standing problem in astronomy. Recently, binary neutron star mergers have been detected by the gravitational wave observations. I will show that they can be the source of such elements in galaxies. I will also present the future prospects of the studies of galactic chemical evolution.