Ryosuke Hirai's Homepage

Research Interests

Supernovae in binaries

My main research interest is on binary stars, especially for high mass stars which explode as core-collapse supernova at the end of their lives. I work intensively on "ejecta-companion interaction", which is the effect of supernova ejecta colliding with a companion star. I have also studied the evolution of binary systems which can reproduce the observed features of a particular supernova iPTF13bvn.

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Hydrodynamical simulations of ejecta-companion interaction (Hirai et al. 2020, Hirai, Podsiadlowski & Yamada 2018, Hirai, Sawai & Yamada 2014).
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Binary evolution simulations for the progenitor of iPTF13bvn (Hirai & Yamada 2015, Hirai 2017a,Hirai 2017b).

Stellar mergers

Stars in binary systems can sometimes lead to catastrophic stellar mergers. I work on modelling the outcome of stellar mergers, specifically for the case of the extraordinary star "Eta Carinae", which was most likely created through a stellar merger in a triple system.

Hydrodynamical simulations of the outflow from stellar merger-induced eruptions and its subsequent super-Eddington wind phase (Hirai et al. 2021).
Combination of triple dynamics calculations and N-body simulations to model the Outer Ejecta of Eta Carinae (Hirai et al. 2021).

Numerical Techniques

Numerical computation is almost inevitable when studying quantitative behaviours of astrophysical phenomena. But we usually have limited computer power, which prevents us from carrying out simulations of the desired resolution. I have investigated how we can improve the computational efficiency of self-gravitational hydrodynamical simulations so that we can speed up simulations.

Test calculation of colliding stars using our "Hyperbolic Self-Gravity Solver" (Hirai, Nagakura, Okawa & Fujisawa 2016).