Neutron stars are ultra-dense objects made of neutrons. They are formed when massive stars die. It is known that two neutron stars sometimes form binary, and if such a case, they finally merge losing energy due to the gravitational waves. Such explosive merger ejects neutron-rich material, and thus, is considered to be a promising site to produce elements by rapid neutron capture nucleosynthesis (r-process).

Radioactive decay of freshly synthesized r-process nuclei heats the ejected material and gives rise to thermal emission in optical to infrared called a "kilonova". In other words, we can obtain information on the elements synthesized in neutron star mergers by observing kilonovae. The elemental information is also important for estimating the properties of the ejecta, becasue the species and amounts of elements synthesized in neutron star mergers depend on the physical conditions such as the temperature and density of the ejecta. Therefore, by observing kilonovae and extracting information of elements from light curves and spectra, it is expected to lead to understanding of the origin of heavy elements as well as the physics of neutron star mergers.

My current research focuses on kilonova spectra, mainly using radiative transfer simulations, to find out how to extract information on individual elements from kilonovae.

Artist’s conception of a neutron star merger and kilonova. ©Tohoku University