Mariko Takahara

Supernova explosions and the soft equation of state

The way in which explosion energy of supernovae E(ex) depends on the softness of the equation of state (EOS) is investigated. As the EOS becomes softer, E(ex) increases significantly until a critical point, after which it decreases rapidly to zero. E(ex) becomes the maximum just before black holes are formed. The extremely soft EOS which induces the strongest explosion is excluded by the constraint that the critical mass of neutron stars, M(cr) derived from the EOS must be greater than the observed mass. The amount of the E(ex) also depends on the shape of EOSs, even if they give the same M(cr). 22 references.

Ciliopathy-associated mutations of IFT122 impair ciliary protein trafficking but not ciliogenesis

The intraflagellar transport (IFT) machinery containing the IFT-A and IFT-B complexes mediates ciliary protein trafficking. Mutations in the genes encoding the six subunits of the IFT-A complex (IFT43, IFT121, IFT122, IFT139, IFT140, and IFT144) are known to cause skeletal ciliopathies, including cranioectodermal dysplasia (CED). As the IFT122 subunit connects the core and peripheral subcomplexes of the IFT-A complex, it is expected to play a pivotal role in the complex. Indeed, we here showed that knockout (KO) of the IFT122 gene in hTERT-RPE1 cells using the CRISPR/Cas9 system led to a severe ciliogenesis defect, whereas KO of other IFT-A genes had minor effects on ciliogenesis but impaired ciliary protein trafficking. Exogenous expression of not only wild-type IFT122 but also its CED-associated missense mutants, which fail to interact with other IFT-A subunits, rescued the ciliogenesis defect of IFT122-KO cells. However, IFT122-KO cells expressing CED-type IFT122 mutants showed defects in ciliary protein trafficking, such as ciliary entry of Smoothened in response to Hedgehog signaling activation. The trafficking defects partially resembled those observed in IFT144-KO cells, which demonstrate failed assembly of the functional IFT-A complex at the base of cilia. These observations make it likely that, although IFT122 is essential for ciliogenesis, CED-type missense mutations underlie a skeletal ciliopathy phenotype by perturbing ciliary protein trafficking with minor effects on ciliogenesis per se.

Constraint on the mass and lifetime of heavy neutrinos from the supernova 1987A in the Large Magellanic Cloud

If heavy neutrinos were emitted from the supernova 1987A in the Large Magellanic Cloud (LMC) and decayed outside the star, a γ-ray burst would have been observed after the ν-burst. If this γ-ray burst was not observed, it would impose a constraint on the mass, mv, and lifetime, τν, of heavy neutrinos. We investigate this constraint on the assumption that the γ-ray burst was not observed and obtain a more stringent constraint than that imposed by cosmology. We find that the range of mass and lifetime of tau neutrinos (mv~50 MeV, τν~103sec), which is allowed by previous constraints from experiments and cosmology, is completely prohibited by the present constraint provided that the radius of the progenitor of this supernova is less than 1013cm.

Effects of Neutrino Trapping on Supernova Explosions

Effects of neutrino trapping on the mass ejection from the stellar cores are investigated with the aid of a simplified equation of state under the assumption of adiabatic collapse. It is found that mass ejection becomes violent only if the ratio of the trapped leptons to baryons, Y L , lies in an appropriate range. If the value of Y L lies out of this range, mass ejection is difficult. It is also shown that as the thermal stiffness of the shocked matter increases, the range necessary for the violent mass ejection becomes wider. Possibilities of supernova explosion are discussed on the basis of these results.