52 research outputs found
Symmetry energy: nuclear masses and neutron stars
We describe the main features of our most recent Hartree-Fock-Bogoliubov
nuclear mass models, based on 16-parameter generalized Skyrme forces. They have
been fitted to the data of the 2012 Atomic Mass Evaluation, and favour a value
of 30 MeV for the symmetry coefficient J, the corresponding root-mean square
deviation being 0.549 MeV. We find that this conclusion is compatible with
measurements of neutron-skin thickness. By constraining the underlying
interactions to fit various equations of state of neutron matter calculated
{\it ab initio} our models are well adapted to a realistic and unified
treatment of all regions of neutron stars. We use our models to calculate the
composition, the equation of state, the mass-radius relation and the maximum
mass. Comparison with observations of neutron stars again favours a value of J
= 30 MeV.Comment: 10 pages, 9 figures, to appear in EPJA special volume on symmetry
energ
Structure of neutron stars with unified equations of state
We present a set of three unified equations of states (EoSs) based on the
nuclear energy-density functional (EDF) theory.These EoSs are based on
generalized Skyrme forces fitted to essentially all experimental atomic mass
data and constrained to reproduce various properties of infinite nuclear matter
as obtained from many-body calculations using realistic two- and three-body
interactions. The structure of cold isolated neutron stars is discussed in
connection with some astrophysical observations.Comment: 4 pages, to appear in the proceedings of the ERPM conference, Zielona
Gora, Poland, April 201
Neutron drip transition in accreting and nonaccreting neutron star crusts
The neutron-drip transition in the dense matter constituting the interior of
neutron stars generally refers to the appearance of unbound neutrons as the
matter density reaches some threshold density . This
transition has been mainly studied under the cold catalyzed matter hypothesis.
However, this assumption is unrealistic for accreting neutron stars. After
examining the physical processes that are thought to be allowed in both
accreting and nonaccreting neutron stars, suitable conditions for the onset of
neutron drip are derived and general analytical expressions for the neutron
drip density and pressure are obtained. Moreover, we show that the neutron-drip
transition occurs at lower density and pressure than those predicted within the
mean-nucleus approximation. This transition is studied numerically for various
initial composition of the ashes from X-ray bursts and superbursts using
microscopic nuclear mass models.Comment: 24 pages, accepted for publication in Physical Review
Giant Pulsar Glitches and the Inertia of Neutron-Star Crusts
Giant pulsar frequency glitches as detected in the emblematic Vela pulsar
have long been thought to be the manifestation of a neutron superfluid
permeating the inner crust of a neutron star. However, this superfluid has been
recently found to be entrained by the crust, and as a consequence it does not
carry enough angular momentum to explain giant glitches. The extent to which
pulsar-timing observations can be reconciled with the standard vortex-mediated
glitch theory is studied considering the current uncertainties on dense-matter
properties. To this end, the crustal moment of inertia of glitching pulsars is
calculated employing a series of different unified dense-matter equations of
state.Comment: 11 pages, 6 figures, submitted to PR
The proto-neutron star inner crust in a multi-component plasma approach
Proto-neutron stars (PNS) are born hot, with temperatures exceeding a few
times K. In these conditions, the PNS crust is expected to be made of
a Coulomb liquid composed of an ensemble of different nuclear species. We
perform a study of the beta-equilibrated PNS crust in the liquid phase in a
self-consistent multi-component plasma (MCP) approach, thus allowing us to
consistently calculate the impurity parameter, often taken as a free parameter
in cooling simulations. We developed a self-consistent MCP approach at finite
temperature using a compressible liquid-drop description of the ions, with
surface parameters adjusted to reproduce experimental masses. The treatment of
the ion centre-of-mass motion was included through a translational free-energy
term accounting for in-medium effects. The results of self-consistent MCP
calculations are systematically compared with those performed in a perturbative
and in the one-component plasma treatment. We show that the inclusion of
non-linear mixing terms arising from the ion centre-of-mass motion leads to a
breakdown of the ensemble equivalence between the one-component and MCP
approach. Our findings illustrate that the abundance of light nuclei becomes
important, eventually dominating the distribution at higher density and
temperature. This is reflected in the impurity parameter, which, in turn, may
have a potential impact on NS cooling. For practical applications, we also
provide a fitting formula for the impurity parameter in the PNS inner crust.
Our results obtained within a self-consistent MCP approach show important
differences in the prediction of the PNS composition with respect to those
obtained with a one-component or a perturbative MCP approximation, particularly
in the deeper region of the crust. This highlights the importance of a full,
self-consistent MCP calculation for reliable predictions of the PNS crust
composition.Comment: 16 pages, 15 figures, accepted for publication in Astronomy and
Astrophysic
Light clusters in the liquid proto-neutron star inner crust
Being born hot from core-collapse supernova, the crust of the proto-neutron
star is expected to be made of a Coulomb liquid and composed of an ensemble of
different nuclear species. In this work, we study the beta-equilibrated
proto-neutron-star crust in the liquid phase in a self-consistent
multi-component approach, employing a compressible liquid-drop description of
the ions including the ion centre-of-mass motion. Particular care is also
devoted to the calculation of the rearrangement term, thus ensuring
thermodynamic consistency. We compare the results of the multi-component plasma
calculations with those obtained within a one-component (single-nucleus)
approach, showing that important differences arise between the predictions of
the two treatments. In particular, the abundances of helium clusters become
important using a complete multi-component plasma approach, and eventually
dominate the whole distribution at higher temperature in the crust.Comment: Submitted to the European Physical Journal A (EPJA) for the Topical
Collection "The Nuclear Many-Body Problem
Masses of neutron stars and nuclei
We calculate the maximum mass of neutron stars for three different equations
of state (EOS) based on generalized Skyrme functionals that are simultaneously
fitted to essentially all the 2003 nuclear mass data (the rms deviation is 0.58
MeV in all three cases) and to one or other of three different equations of
state of pure neutron matter, each determined by a different many-body
calculation using realistic two- and three-body interactions but leading to
significantly different degrees of stiffness at the high densities prevailing
in neutron-star interiors. The observation of a neutron star with mass 1.97
0.04 eliminates the softest of our models (BSk19),
but does not discriminate between BSk20 and BSk21. However, nuclear-mass
measurements that have been made since our models were constructed strongly
favor BSk21, our stiffest functional.Comment: 11 pages, 4 figures; Physical Review C in pres
Symmetry energy and composition of the outer crust of neutron stars
In this paper, we study the role of the symmetry energy on the composition of the outer crust of a neutron star. Although some correlations can be observed at the neutron-drip transition, the composition of the outer crust is mainly sensitive to the details of the nuclear structure far from the valley of stability rather than to the symmetry energy only
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