Polycrystalline Crusts in Accreting Neutron Stars

M. E. Caplan, Andrew Cumming, D. K. Berry, C. J. Horowitz, R. McKinven

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


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. In this paper, we explore 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 results motivate further work on the size of the compositional domains and have implications for crust physics and accreting neutron star phenomenology.

Original languageEnglish
Article number148
JournalAstrophysical Journal
Issue number2
StatePublished - 20 Jun 2018
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved..


This research was supported by Lilly Endowment, Inc., the Indiana University Pervasive Technology Institute, and the Indiana METACyt Initiative at Indiana University, and DOE grants DE-FG02-87ER40365 (Indiana University) and DESC0008808 (NUCLEI SciDAC Collaboration). M.C. is a CITA National Fellow. A.C.is supported by an NSERC Discovery grant. A.C.and M.C.are members of the Centre de Recherche en Astrophysique du Québec, and thank Newcastle University for hospitality.

FundersFunder number
Indiana University Pervasive Technology Institute
Lilly Endowment, Inc.
U.S. Department of EnergyDE-FG02-87ER40365
Indiana UniversityDESC0008808
Natural Sciences and Engineering Research Council of Canada


    • X-rays: binaries
    • X-rays: bursts
    • accretion, accretion disks
    • dense matter
    • stars: interiors
    • stars: neutron


    Dive into the research topics of 'Polycrystalline Crusts in Accreting Neutron Stars'. Together they form a unique fingerprint.

    Cite this