National Astronomical Observatory of Japan

Classical Nova Explosions are Major Lithium Factories in the Universe

| Science

A team of astronomers from National Astronomical Observatory of Japan (NAOJ), Osaka Kyoiku University, Nagoya University, and Kyoto Sangyo University observed Nova Delphini 2013 which occurred on August 14, 2013. Using the 8.2-meter Subaru Telescope High Dispersion Spectrograph (HDS) to observe this object, they discovered that the outburst is producing a large amount of lithium (Li; Note). Lithium is a key element in the study of the chemical evolution of the universe because it likely was and is produced in several ways: through Big Bang nucleosynthesis, in collisions between energetic cosmic rays and the interstellar medium, inside stellar interiors, and as a result of novae and supernova explosions. This new observation provides the first direct evidence for the supply of Li from stellar objects to the galactic medium. The team hopes to deepen the understandings of galactic chemical evolution, given that nova explosions must be important suppliers of Li in the current universe.

Note: Lithium is composed of two stable isotopes -- 6Li and 7Li. In the solar system, about 92 percent of Li is 7Li. In this press release, "Li" means the most abundant 7Li.

This research was published in Nature on February 19, 2015, titled "Explosive lithium production in the classical nova V339 Del (Nova Delphini 2013)".

Figure 1
Artist's rendition of a classical nova explosion
A classical nova explosion is thought to occur on the surface of a white dwarf (center right) with a close companion star (center left; a sun-like main sequence or more evolved star). When the distance between two stars is close enough, the outer gas of the companion starts to accumulate on the surface of the white dwarf via an accretion disk. The thicker gas layer on the white dwarf increases its temperature and density. Then, nuclear reactions occur with a different way from those inside stars. In the case of stellar interiors, the huge energy produced by nuclear reactions in the core is balanced by the gravity of the surrounding gas, and then the reaction becomes stable. However, the nuclear reaction in a thin gas layer on the surface of a white dwarf has a different result. It becomes a runaway nuclear reaction, and results in an explosion that blows away the gas layer.