Subaru Telescope: 20 Years of Observing the Heavens

The origins of some elements remain unknown. Such elements include Lithium, the third lightest element after hydrogen and helium, and elements heavier than iron, like gold and platinum. The Subaru Telescope showed that these elements are produced in stellar explosions. When a close binary star system contains a white dwarf and gas falls onto the white dwarf, it can cause an explosion called a nova. Observations using the High Dispersion Spectrograph (HDS) proved that lithium was produced in a nova known as V339 Delphini, suggesting for the first time that nova explosions are the Universe’s lithium factories.

Among the elements heavier than iron, those produced by rapid neutron-capture processes (r-processes) were thought to have been synthesized by merging neutron stars. The Subaru Telescope used Hyper Suprime-Cam (HSC) and the Multi-Object Infrared Camera and Spectrograph (MOIRCS) to conduct optical-infrared follow-up observations of radiation associated with the gravitational wave source GW170817, and from its characteristics, found evidence that a large amount of r-process elements were produced.

What was the very first star in the Universe like? One of the ways to answer this question is to find old stars that were born in the early Universe and have survived to today, and to analyze their detailed characteristics. HDS mounted on the Subaru Telescope revealed that a star called SDSS J0018-0939 is just such a star. This star may have been created from gas ejected by supernova explosions of first-generation stars.