The University of Tokyo · Physics and Astronomy
Professor K. Nomoto's research lab specializes in theoretical astrophysics, focusing on the life cycles and explosive deaths of massive stars, particularly the formation and evolution of white dwarfs, supernovae, and the nucleosynthesis of heavy elements in the early universe. The lab investigates supernova mechanisms such as carbon deflagration, electron capture in O+Ne+Mg cores, and accretion-induced collapse (AIC) of white dwarfs, linking these processes to observed elemental abundances in metal-poor stars. A central theme is understanding the origins of Type Ia and electron-capture supernovae, as well as the role of first-generation stars in enriching the cosmos with heavy elements.
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The carbon deflagration models in accreting C + O white dwarfs are presented as a plausible model for Type I supernovae. The evolution of the white dwarf is calculated from the beginning of accretion. The relatively rapid accretion studied here (Mdot > 4 x 10<SUP>-8</SUP> Msun yr<SUP>-1</SUP>) leads to the initiation of the carbon deflagration at the center. Subsequent propagation of the convective carbon deflagration wave and associated explosive nucleosynthesis are calculated for several ca
After the Big Bang, production of heavy elements in the early Universe takes place starting from the formation of the first stars, their evolution, and explosion. The first supernova explosions have strong dynamical, thermal, and chemical feedback on the formation of subsequent stars and evolution of galaxies. However, the nature of the Universe's first stars and supernova explosions has not been well clarified. The signature of the nucleosynthesis yields of the first stars can be seen in the el
Results are presented of numerical calculations of the presupernova evolution and triggering mechanisms of accreting white dwarf stars, which have been suggested as the progenitors of type I supernovae. The evolution of carbon-oxygen white dwarf models accreting helium in binary systems was computed using a Henyey-type hybrid method including both thermal and hydrodynamical equations. It is found that type I supernovae can be triggered by the off-center detonation of helium in systems with slow
view Abstract Citations (583) References (77) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evolution of 8-10 solar mass stars toward electron capture supernovae. I - Formation of electron-degenerate O + NE + MG cores. Nomoto, K. Abstract One triggering mechanism suggested for supernovae involves the collapse of a degenerate core due to electron captures. Barkat et al. (1974) showed that an eight solar mass star develops a degenerate core after nonexplosive car
Recent discovery of an unexpectedly large number of low-mass binary pulsars (LMBPs) in globular clusters has instigated active discussions on the evolutionary origin of binary pulsars. Prompted by the possibility that at least some of LMBPs originate from accretion-induced collapse (AIC) of white dwarfs, a reexamination is conducted as to whether or not AIC occurs for the new models of O + Ne + Mg white dwarfs and solid C + O white dwarfs that can ignite explosive nuclear burning at significantl
In this paper, the helium core of an 8.8 solar mass star is evolved from the helium-burning stage through the early stage of collapse of an O + Ne + Mg core. The star undergoes helium and carbon burning under nondegenerate conditions and leaves an O + Ne + Mg core. The penetration of the surface convection zone into the helium layer starts much earlier than in a 9.6 solar mass star studied elsewhere. The subsequent evolution is brought about by hydrogen-helium double-shell burning. The mass inte
The hydrodynamical behavior of supernova models based on accreting carbon-oxygen white dwarfs is computed through the explosion for three cases with different accretion rates. For intermediate accretion rates, the helium flash is so strong that it produces a helium detonation wave propagating outward and a carbon detonation wave propagating inward, which results in most of the star's material being converted into N-56 and the star itself being completely disrupted. For the case with a slower acc
Recent studies have suggested that the merging of two degenerate dwarfs composed of carbon and oxygen and of total mass larger than the Chandrasekhar limit occurs at a frequency comparable to that of Type I supernovae. The rate at which mass is transferred in the merging process is at present unknown, except that it must be less than some appropriate Eddington limit. It is found that, unless mass transfer occurs at a rate less than one-fifth of the Eddington limit for an isolated dwarf, carbon i
The recent discovery of a hyper-metal-poor (HMP) star, with a metallicity Fe/H smaller than 1/100,000 of the solar ratio, together with one earlier HMP star, has raised a challenging question whether these HMP stars are the actual first-generation, low-mass stars of the universe. We argue that these HMP stars are second-generation stars formed from gases that were chemically enriched by the first-generation supernovae. The key to this solution is the very unusual abundance patterns of these HMP
We revisit the properties of white dwarfs accreting hydrogen-rich matter by constructing steady-state models, in which hydrogen shell burning consumes hydrogen at the same rate as the white dwarf accretes it. We obtain such steady-state models for various accretion rates and white dwarf masses. We confirm that these steady models are thermally stable only when the accretion rate is higher than \sim 10^{-7} M_sun/yr. We show that recent models of ``quiescent burning'' in the ``surface hydrogen bu
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