Division of Theoretical Astronomy, National Astronomical Observatory of Japan

Research Highlights

Little Supernova is Big Discovery: the Origin of Binary Neutron Stars

An international research team including Takashi Moriya at DTA/NAOJ discovered the first recorded "ultra-stripped supernova," a rare, faint type of supernova that is believed to play a role in the formation of binary neutron star systems. These findings will advance our understanding of a wide variety of topics ranging from gravitational waves to the origin of precious metals like gold and platinum. This research was published in Science on October 12, 2018.

See the full story: DTA Press Release "Little Supernova is Big Discovery: the Origin of Binary Neutron Stars"

Figure: Red and green composite image from the Sloan Digital Sky Survey (SDSS) taken before supernova iPTF14gqr. Right: Red/green/blue composite image from the Palomar 60-inch telescope taken on October 19, 2014, during supernova iPTF14gqr. The circles indicate the position of the supernova. (Credit: SDSS/Caltech)

"A hot and fast ultra-stripped supernova that likely formed a compact neutron star binary"
K. De, M. M. Kasliwal, E. O. Ofek, T. J. Moriya et al., Science, Vol. 362, Issue 6411, pp. 201-206

Takashi Moriya (personal website)

Cosmochronometer 98Tc is produced abundantly by supernova electron antineutrinos

An international collaboration including Toshitaka Kajino and Motohiko Kusakabe (2018 NAOJ Visiting Professor) in the COSNAP group found that the short-lived nuclide 98Tc is produced significantly by reactions of electron antineutrinos with nuclei in supernovae. In the end of massive stellar evolution, supernovae occur and an extremely large number of neutrinos and antineutrinos are emitted from a neutron star in the center. The collaboration group calculated nucleosynthesis of 98Tc in supernovae taking into account neutrino and antineutrino reactions of preexisting nuclei. It was then shown that the charged-current anti-neutrino reactions significantly contribute to the production of 98Tc in supernovae. The 98Tc is the first nuclide whose production was found to be sensitive to the antineutrino energy spectrum. It is a potential chronometer for the time between the last supernova before the solar system formation and the meteoritic formation. Therefore, future measurements of its meteoritic abundance can be used to deduce the antineutrino spectrum and the time scale of the meteoritic formation.
Figure: Cosmic clocks. We can estimate the age of heavy elements in the primordial Solar System by measuring the traces left in meteorites by specific radioactive nuclei synthesized in certain types of supernovae. (Credit: NAOJ)

Details will be found in NAOJ web site .

Toshitaka Kajino (personal website)

Nucleosynthesis Constraints on the Explosion Mechanism for Type Ia Supernovae

Type Ia supernovae (SNe Ia) play important roles in cosmology as a standard candle, although their progenitors and explosion mechanisms have been a long-standing mystery. One possible solution is to compare theoretical and observational nucleosynthetic yields, which needs careful collaboration among theories, observations, and experiments of astronomy and nuclear physics. Recent observations have revealed the abundances of radioactive elements including manganese, cobalt, iron, and nickel. We perform collaboration among researchers on supernova theories, astronomical observations, and experimental nuclear physics to calculate these abundances precisely. Comparison between the observed and the calculated isotopic ratios shows the way to diagnose explosion mechanisms of SNe Ia. In addition to that, it is pointed out that yields of some neutron-rich nuclei are good indicators of the density, therefore can constrain progenitors and explosion mechanisms if they are observed.

Figure: Elemental ratios of iron group elements from observations of supernova remnants and model calculations.

"Nucleosynthesis Constraints on the Explosion Mechanism for Type Ia Supernovae"
K. Mori, M. A. Famiano, T. Kajino, T. Suzuki, P. Garnavich, G. J. Mathews, R. Diehl, S. -C. Leung and K. Nomoto, The Astrophysical Journal, 863, 176

Kanji Mori

Veiled Supernovae Provide Clue to Stellar Evolution

At the end of its life, a red supergiant star explodes in a hydrogen-rich supernova. By comparing observation results to simulation models, an international research team including Takashi Moriya at DTA/NAOJ found that in many cases this explosion takes place inside a thick cloud of circumstellar matter shrouding the star. This result completely changes our understanding of the last stage of stellar evolution. This research was published in Nature Astronomy on September 3, 2018.

Figure: Artist's impression of a red supergiant surrounded with thick circumstellar matter. (Credit: NAOJ)

See the full story: DTA Press Release "Veiled Supernovae Provide Clue to Stellar Evolution"

"The delay of shock breakout due to circumstellar material evident in most type II supernovae"
F. Förster, T. J. Moriya et al. (2018) Nature Astronomy

Takashi Moriya (personal website)

Why are we all left handed? – Theory of elementary particle origin

International collaboration team among scientists at NAOJ, The University of Tokyo, Western Michigan University and Ohio State University has come up with a possible way in which Mother Nature selects left-handed amino acids in space. This new theory brings together fundamental particle physics, electromagnetism, biology, and chemistry. Molecules in magnetic fields can interact with leptons (some of the tiniest particles in nature which include electrons and neutrinos). Neutrino chirality is completely broken. Because leptons can also be chiral, they interact with amino acids differently depending on the combination of lepton chirality and amino acid chirality. This interaction can selectively destroy one mirror image more than the other, resulting in the imbalance that we see in meteorites. Since Louis Pasteur studied molecular chirality nearly 170 years ago, a question how amino acids got to be left-handed is one of the biggest questions in science. Not only does this discovery predict how amino acids got to be left-handed, it also predicts how they became left-handed in space. The ramifications for life on the earth and elsewhere in the cosmos are significant. The latest news on this discovery was published in Scientific Reports (a Nature journal) on Monday, June 11 at 10am GMT.

Illustration: The amino acid alanine in its left-handed form and right-handed form. The grey, red, blue, and white spheres are carbon, oxygen, nitrogen, and hydrogen respectively.

See also this link

"Amino Acid Chiral Selection Via Weak Interactions in Stellar Environments: Implications for the Origin of Life" Famiano M.A., Boyd, R.N, Kajino, T., Onaka, T., & Mo, Y., Scientific Reports, vol 8. (2018)

"Selection of Amino Acid Chirality via Neutrino Interactions with 14N in Crossed Electric and Magnetic Fields" Famiano, M.A., Boyd, R.N., Kajino, T., & Onaka, T., Astrobiology 18, 190 (2018).

Toshitaka Kajino (personal website)

New simulations of terrestrial planet formation

It is widely accepted that planets form in a gaseous disk (or a protoplanetary disk) that surrounds the star. As the disk affects planet formation processes in several ways, the evolution and property of the disk is crucial in studying the planet formation. We study formation of terrestrial planets by numerical simulations that take into account recent developments of the disk evolution theory (e.g., magnetically driven disk winds). We found that the localized configuration of the terrestrial planets of the solar system can be reproduced by the radial drift of small bodies due to the effect of disk winds. We also showed that the origin of observed properties of close-in super-Earths can be explained by considering the realistic evolution of a protoplanetary disk (see figure).

Ogihara, Kokubo et al. 2018, A&A, 612, L5
[ADS] [arXiv]

Ogihara, Kokubo et al. 2018, A&A, in press
[ADS] [arXiv]

Masahiro Ogihara (personal website)