Division of Theoretical Astronomy, National Astronomical Observatory of Japan

Research Highlights

Surface Helium Detonation Spells End for White Dwarf

An international team of researchers has found evidence that the brightest stellar explosions in our Universe could be triggered by helium nuclear detonation near the surface of a white dwarf star. Using Hyper Suprime-Cam mounted on the Subaru Telescope, the team detected a type Ia supernova within a day after the explosion, and explained its behavior through a model calculated using the supercomputer ATERUI. This result was reported in Nature published on Oct. 5.
See the full story:
Subaru Telescope Press Release: "Surface Helium Detonation Spells End for White Dwarf"
CfCA Press Release: "Surface Helium Detonation Spells End for White Dwarf"

Figure: A type Ia supernova detected within a day after exploding. Taken with Hyper Suprime-Cam mounted on the Subaru Telescope. (Credit: The University of Tokyo / NAOJ)

"A hybrid type la supernova with an early flash triggered by helium-shell detonation"
Jiang et al., 2017, Nature 550, 80–83 [Nature]
Masaomi Tanaka [personal webpage]

The effect of collective neutrino oscillations on vp process nucleosynthesis

In core collapse supernovae, large numbers of neutrinos are emitted from the protoneutron star after core bounce. At such high neutrino number densities, neutrino-neutrino coherent scatterings cause a non-linear phenomenon called "collective neutrino oscillation" which results in the dramatic flavor transition in neutrino and antineutrino spectra. There was no quantitative study which took into account the influence of collective neutrino oscillations on the vp-process nucleosynthesis consistently. In this work, we study the impact of collective neutrino oscillations on the vp process nucleosynthesis by combining realistic three flavor multiangle simulations with nucleosynthesis network calculations for the first time. We find that the abundances of p-nuclei which are synthesized in the vp process are enhanced by oscillation effects by 10-10^4 times in normal mass hierarchy. Our results imply the necessity of collective neutrino oscillations for the precise nucleosynthesis in neutrino-driven winds and also help understand the origin of solar-system isotopic abundances of molybdenum 92,94 and ruthenium 96,98.

Figure: The abundances of p-nuclei inside neutrino-driven winds which are normalized by solar isotopic abundances. In normal mass hierarchy (red point), the abundances of p-nuclei are enhanced by collective neutrino oscillations compared with no oscillation case (black point).

"Possible effects of collective neutrino oscillations in three-flavor multiangle simulations of supernova vp processes"
Hirokazu Sasaki, Toshitaka Kajino, Tomoya Takiwaki, Takehito Hayakawa, Baha Balantekin, and Yamac Pehlivan
2017, Physical Review D, 96, 043013 [PRD] [arXiv]
Hirokazu Sasaki