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Title: Polycrystalline Crusts in Accreting Neutron Stars

Abstract

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.

Authors:
 [1]; ORCiD logo [1];  [2];  [2]; ORCiD logo [3]
  1. McGill Univ., Montreal, QC (Canada). Dept of Physics
  2. Indiana Univ., Bloomington, IN (United States)
  3. Univ. of Toronto, ON (Canada)
Publication Date:
Research Org.:
Indiana Univ., Bloomington, IN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
OSTI Identifier:
1542026
Grant/Contract Number:  
FG02-87ER40365; SC0008808
Resource Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 860; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; accretion; accretion disks; dense matter; stars: interiors; stars: neutron; X-rays: binaries; X-rays: bursts

Citation Formats

Caplan, Matthew E., Cumming, Andrew, Berry, D. K., Horowitz, C. J., and Mckinven, R. Polycrystalline Crusts in Accreting Neutron Stars. United States: N. p., 2018. Web. doi:10.3847/1538-4357/aac2d2.
Caplan, Matthew E., Cumming, Andrew, Berry, D. K., Horowitz, C. J., & Mckinven, R. Polycrystalline Crusts in Accreting Neutron Stars. United States. doi:10.3847/1538-4357/aac2d2.
Caplan, Matthew E., Cumming, Andrew, Berry, D. K., Horowitz, C. J., and Mckinven, R. Thu . "Polycrystalline Crusts in Accreting Neutron Stars". United States. doi:10.3847/1538-4357/aac2d2. https://www.osti.gov/servlets/purl/1542026.
@article{osti_1542026,
title = {Polycrystalline Crusts in Accreting Neutron Stars},
author = {Caplan, Matthew E. and Cumming, Andrew and Berry, D. K. and Horowitz, C. J. and Mckinven, R.},
abstractNote = {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.},
doi = {10.3847/1538-4357/aac2d2},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 860,
place = {United States},
year = {2018},
month = {6}
}

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