U.S.-Japan Cooperative Research: Phase Transitions in Dense Astrophysical Plasmas

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This award provides support for a two year cooperative research project on dense astrophysical plasmas, between Professor Hugh M Van Horn, Department of Physics and Astronomy, University of Rochester, and Professor Setsuo Ichimaru, Department of Physics, University of Tokyo, Japan. In dense astrophysical objects, such as neutron stars, white dwarfs, low mass stars (brown dwarfs), the solar interior, and giant planets, collections of ionized nuclei and electrons constitute dense plasmas, which exhibit various kinds of phase changes. In recent years, due to advancements in condensed-matter theories coupled with progress in computer-simulation capabilities, it has become possible to carry out detailed analyses of those phase-transition processes in dense astrophysical plasmas. The aim of this proposal is to undertake theoretical and computer-simulation studies on a number of those phase transition processes. The processes to be studied include: (1) the possibility that neutron stars may have glassy rather than crystalline crusts, and what the consequences are of that; (2) the possibilities of phase separation in binary carbon/oxygen and iron/carbon mixtures, which have been suggested as energy sources in very cool white dwarfs; (3) iron/hydrogen phase separation, which may have interesting consequences for the evolution of low mass stars and "brown dwarfs"; and (4) hydrogen/helium phase separation in giant planets and brown dwarfs, which may prove a significant energy source in these bodies. The two groups involved in this collaboration complement each other well. The Japanese scientists have a long history of important contributions in areas of dense plasma physics and condensed matter physics relevant to this collaboration, and also have a strong interest in astrophysical applications. The US group has a similar interest in astrophysics, together with a strong interest in the relevant properties of matter at high densities. If successful this project will make a significant contribution to research problems at the interface between the disciplines of dense plasma physics, condensed matter physics and astrophysics.