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          Institute: MPI für Gravitationsphysik     Collection: Observational Relativity and Cosmology     Display Documents



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ID: 379331.0, MPI für Gravitationsphysik / Observational Relativity and Cosmology
Slowly rotating superfluid Newtonian neutron star model with entrainment
Authors:Prix, Reinhard; Andersson, Nils; Comer, G. L.
Date of Publication (YYYY-MM-DD):2002-01
Title of Journal:Astronomy and Astrophysics
Volume:381
Issue / Number:1
Start Page:178
End Page:196
Review Status:not specified
Audience:Not Specified
Abstract / Description:We develop a formalism that can be used to model slowly rotating superfluid Newtonian neutron stars. A simple two-fluid model is used to describe the matter, where one fluid consists of the superfluid neutrons that are believed to exist in the inner crust and core of mature neutron stars, while the other fluid is a charge neutral conglomerate of the remaining constituents (crust nuclei, core superconducting protons, electrons, etc.). We include the entrainment effect, which is a non-dissipative interaction between the two fluids whereby a momentum induced in one of the fluids will cause part of the mass of the other fluid to be carried along. The equations that describe rotational equilibria (i.e. axisymmetric and stationary configurations) are approximated using the slow-rotation approximation; an expansion in terms of the rotation rates of the two fluids where only terms up to second-order are kept. Our formalism allows the neutrons to rotate at a rate different from that of the charged constituents. For a particular equation of state that is quadratic in the two mass-densities and relative velocities of the fluids, we find an analytic solution to the slow-rotation equations. This result provides an elegant generalisation to the two-fluid problem of the standard expressions for the one-fluid polytrope ${\cal E} \propto \rho^2$. The model equation of state includes entrainment and is general enough to allow for realistic values for, say, mass and radius of the star. It also includes a mixed term in the mass densities that can be related to "symmetry energy" terms that appear in more realistic equations of state. We use the analytic solution to explore how relative rotation between the two fluids, the "symmetry energy" term, and entrainment affect the neutron star's local distribution of particles, as well as global quantities as the Kepler limit, ellipticity, and moments of inertia.
External Publication Status:published
Document Type:Article
Communicated by:Bruce Allen
Affiliations:MPI für Gravitationsphysik/Teilinstitut Hannover
MPI für Gravitationsphysik/Observational Relativity and Cosmology
Identifiers:LOCALID:arXiv:astro-ph/0107176v1
DOI:10.1051/0004-6361:20011499
ISSN:0004-6361
URL:http://arxiv.org/abs/astro-ph/0107176
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