Phase separation in the crust of accreting neutron stars

Horowitz, C. J.; Berry, Don; Brown, Edward F.

doi:10.1103/physreve.75.066101

Cited by 86 publications

(173 citation statements)

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“…II A we describe our two-phase MD simulation formalism. This is very similar to what we used earlier for the freezing of rapid proton capture nucleosynthesis ash on accreting neutron stars [10] and for carbon and oxygen mixtures in WDs [26]. Next, in Sec.…”

Section: Formalismsupporting

confidence: 49%

“…A variety of nuclear reactions can take place, including rapid proton capture nucleosynthesis (the rp process [8,9]) followed by electron captures, as the material is advected to higher densities. Horowitz et al studied the crystallization of a complex rp process ash consisting of 17 chemical elements from oxygen to selenium [10]. They found chemical separation upon freezing, with low Z elements preferentially remaining in the liquid NS ocean while high Z elements crystallize to form new NS crust.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, we performed direct two-phase molecular dynamics simulations of liquid-solid phase equilibria both for carbon-oxygen mixtures in WDs [26] and for a complex 17-component mixture modeling the crust of an accreting neutron star [10]. These simulations have both liquid and solid phases present simultaneously.…”

Section: Introductionmentioning

confidence: 99%

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Direct molecular dynamics simulation of liquid-solid phase equilibria for two-component plasmas

et al. 2012

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We determine the liquid-solid phase diagram for carbon-oxygen and oxygen-selenium plasma mixtures using two-phase molecular dynamics simulations. We identify liquid, solid, and interface regions using a bond angle metric. To study finite-size effects, we perform 27 648-and 55 296-ion simulations. To help monitor nonequilibrium effects, we calculate diffusion constants D i . For the carbon-oxygen system we find that D O for oxygen ions in the solid is much smaller than D C for carbon ions and that both diffusion constants are 80 or more times smaller than diffusion constants in the liquid phase. There is excellent agreement between our carbon-oxygen phase diagram and that predicted by Medin and Cumming. This suggests that errors from finite-size and nonequilibrium effects are small and that the carbon-oxygen phase diagram is now accurately known. The oxygen-selenium system is a simple two-component model for more complex rapid proton capture nucleosynthesis ash compositions for an accreting neutron star. Diffusion of oxygen, in a predominantly selenium crystal, is remarkably fast, comparable to diffusion in the liquid phase. We find a somewhat lower melting temperature for the oxygen-selenium system than that predicted by Medin and Cumming. This is probably because of electron screening effects.

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Section: Formalismsupporting

confidence: 49%

Section: Introductionmentioning

confidence: 99%

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Direct molecular dynamics simulation of liquid-solid phase equilibria for two-component plasmas

et al. 2012

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“…We identified liquid, solid, and interface regions in our simulations using a bond angle metric described in Section II B. This is the latest in a series of papers on liquid-solid equilibria both for complex multicomponent rp ash systems on accreting neutron stars [19] and for two component carbon-oxygen systems in cooling white dwarfs [4,18].…”

Section: Discussionmentioning

confidence: 99%

“…Recently, we have performed direct two-phase molecular dynamics simulations of liquid-solid phase equilibria for carbon-oxygen mixtures in WD stars [4,18], oxygen-selenium mixtures [18], and for a complex 17 component mixture modeling the crust of an accreting neutron star [19]. These simulations have both liquid and solid phases present simultaneously.…”

Section: Introductionmentioning

confidence: 99%

Direct molecular dynamics simulation of liquid-solid phase equilibria for a three-component plasma

et al. 2012

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The neutron rich isotope 22 Ne may be a significant impurity in carbon and oxygen white dwarfs and could impact how the stars freeze. We perform molecular dynamics simulations to determine the influence of 22 Ne in carbon-oxygen-neon systems on liquid-solid phase equilibria. Both liquid and solid phases are present simultaneously in our simulation volumes. We identify liquid, solid, and interface regions in our simulations using a bond angle metric. In general we find good agreement for the composition of liquid and solid phases between our MD simulations and the semi analytic model of Medin and Cumming. The trace presence of a third component, neon, does not appear to strongly impact the chemical separation found previously for two component carbon and oxygen systems. This suggests that small amounts of 22 Ne may not qualitatively change how the material in white dwarf stars freezes. However, we do find systematically lower melting temperatures (higher Γ) in our MD simulations compared to the semi analytic model. This difference seems to grow with impurity parameter Qimp and suggests a problem with simple corrections to the linear mixing rule for the free energy of multicomponent solid mixtures that is used in the semi analytic model.

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Investigating the Performance of LLVM-Based Intel Fortran Compiler (ifx)

Ruhela

2024

Lecture Notes in Computer Science

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Phase separation in the crust of accreting neutron stars

Cited by 86 publications

References 20 publications

Direct molecular dynamics simulation of liquid-solid phase equilibria for two-component plasmas

Direct molecular dynamics simulation of liquid-solid phase equilibria for two-component plasmas

Direct molecular dynamics simulation of liquid-solid phase equilibria for a three-component plasma

Investigating the Performance of LLVM-Based Intel Fortran Compiler (ifx)

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