Polycrystalline Crusts in Accreting Neutron Stars

Journal Article · 21 June 2018 · The Astrophysical Journal (Online)

DOI: https://doi.org/10.3847/1538-4357/aac2d2 · OSTI ID:1542026

Caplan, Matthew E. ^[1]; Cumming, Andrew  ^[1]; Berry, D. K. ^[2]; Horowitz, C. J. ^[2]; Mckinven, R.  ^[3]

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1. McGill Univ., Montreal, QC (Canada). Dept of Physics
2. Indiana Univ., Bloomington, IN (United States)
3. Univ. of Toronto, ON (Canada)

The crust of accreting neutron stars plays a central role in many different observational phenomena. In these stars, heavy elements produced by H–He burning in the rapid proton capture (rp-) process continually freeze to form new crust. Here, we investigate the expected composition of the solid phase. We first demonstrate using molecular dynamics that two distinct types of chemical separations occur, depending on the composition of the rp-process ashes. We then calculate phase diagrams for three-component mixtures and use them to determine the allowed crust compositions. We show that, for the large range of atomic numbers produced in the rp-process (Z ~ 10–50), the solid that forms has only a small number of available compositions. We conclude that accreting neutron star crusts should be polycrystalline, with domains of distinct composition. Our findings motivate further work on the size of the compositional domains and have implications for crust physics and accreting neutron star phenomenology.

• Research Organization: Indiana Univ., Bloomington, IN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• Grant/Contract Number: FG02-87ER40365; SC0008808
• OSTI ID: 1542026
• Journal Information: The Astrophysical Journal (Online), Vol. 860, Issue 2; ISSN 1538-4357
• Publisher: Institute of Physics (IOP)Copyright Statement
• Country of Publication: United States
• Language: English