J/A+A/633/A149 Crystallization of neutron star outer crust (Fantina+, 2020)
Crystallization of the outer crust of a non-accreting neutron star.
Fantina A.F., de Ridder S., Chamel N., Gulminelli F.
<Astron. Astrophys. 633, A149 (2020)>
=2020A&A...633A.149F 2020A&A...633A.149F (SIMBAD/NED BibCode)
ADC_Keywords: Pulsars ; Atomic physics
Keywords: stars: neutron - dense matter -
nuclear reactions, nucleosynthesis, abundances - plasmas
Abstract:
The interior of a neutron star is usually assumed to be made of cold
catalyzed matter. However, the outer layers are unlikely to remain in
full thermodynamic equilibrium during the formation of the star and
its subsequent cooling, especially after crystallization occurs.
We study the cooling and the equilibrium composition of the outer
layers of a non-accreting neutron star down to crystallization. Here
the impurity parameter, generally taken as a free parameter in cooling
simulations, is calculated self-consistently using a microscopic
nuclear model for which a unified equation of state has recently been
determined.
We follow the evolution of the nuclear distributions of the
multi-component Coulomb liquid plasma fully self-consistently,
adapting a general formalism originally developed for the description
of supernova cores. We calculate the impurity parameter at the
crystallization temperature as determined in the one-component plasma
approximation.
Our analysis shows that the sharp changes in composition obtained in
the one-component plasma approximation are smoothed out when a full
nuclear distribution is allowed. The Coulomb coupling parameter at
melting is found to be reasonably close to the canonical value of 175,
except for specific values of the pressure for which supercooling
occurs in the one-component plasma approximation. Our multi-component
treatment leads to non-monotonic variations of the impurity parameter
with pressure. Its values can change by several orders of magnitude
reaching about 50, suggesting that the crust may be composed of an
alternation of pure (highly conductive) and impure (highly resistive)
layers. The results presented here complement the recent unified
equation of state obtained within the same nuclear model.
Our self-consistent approach to hot dense multi-component plasma shows
that the presence of impurities in the outer crust of a neutron star
is non- negligible and may have a sizeable impact on transport
properties. In turn, this may have important implications not only for
the cooling of neutron stars, but also for their magneto-rotational
evolution.
Description:
The impurity parameter obtained in a self-consistent multi-component
plasma approach at equilibrium is presented.
For each value of pressure in the range relevant for the outer crust
of a non-accreting neutron star, the crystallization temperature and
the impurity parameter at the crystallization temperature are given.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
qimp-tm.dat 36 1461 Pressure, melting temperature, impurity parameter
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Byte-by-byte Description of file: qimp-tm.dat
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Bytes Format Units Label Explanations
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1- 10 E10.4 dPa P Pressure (1)
14- 23 E10.4 K Tm Crystallization temperature
27- 36 E10.4 --- Qimp Impurity parameter at Tm (dimensionless)
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Note (1): The SI unit dPa is equivalent to the CGS unit erg/cm3 or equivalent
to dyn/cm2. The conversion factor between the nuclear units for the pressure
(MeV/fm3) and the SI unit dPa is 1.6021766e+33.
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Acknowledgements:
Anthea F. Fantina, anthea.fantina(at)ganil.fr
References:
Goriely, Chamel, & Pearson, 2013PhRvC..88b4308G 2013PhRvC..88b4308G;
Pearson, Chamel, Potekhin, Fantina, Ducoin, Dutta & Goriely,
2018MNRAS.481.2994P 2018MNRAS.481.2994P
(End) Anthea F. Fantina [GANIL], Patricia Vannier [CDS] 02-Dec-2019