706 research outputs found
Spin Clustering of Accreting X-ray Neutron Stars as Possible Evidence of Quark Matter
A neutron star in binary orbit with a low-mass non-degenerate companion
becomes a source of x-rays with millisecond variability when mass accretion
spins it up. Centrifugally driven changes in density profile may initiate a
phase transition in a growing region of the core parallel to what may take
place in an isolated millisecond pulsar, but in reverse. Such a star will spend
a longer time in the spin frequency range over which the transition occurs than
elsewhere because the change of phase, paced by the spinup rate, is accompanied
by a growth in the moment of inertia. The population of accreters will exhibit
a clustering in the critical frequency range. A phase change triggered by
changing spin and the accompanying adjustment of moment of inertia has its
analogue in rotating nuclei.Comment: 5 pages (AIPproc latex) 6 figures. To be presented at the
International Conference on Nuclear Physics, 30 July - 3 August 2001,
Berkeley, Californi
Comment on ``Signal of Quark Deconfinement in the Timing Structure of Pulsar Spin-Down''
This is a comment on a paper by Glendenning, Pei, and Weber (Phys. Rev.
Lett., 79, 1603, 1997), where the authors gave an incorrect estimate of the
event rate and neglected the important gravitational energy release. Previous
work on the same subject is reviewed, and a new suggestion is made to link
quark-hadron phase transitions with soft gamma-ray repeaters.Comment: 4 pages; to appear in Phys. Rev. Let
Properties of Magnetized Quark-Hybrid Stars
The structure of a magnetized quark-hybrid stars (QHS) is modeled using a
standard relativistic mean-field equation of state (EoS) for the description of
hadronic matter. For quark matter we consider a bag model EoS which is modified
perturbatively to account for the presence of a uniform magnetic field. The
mass-radius (M-R) relationship, gravitational redshift and rotational Kepler
periods of such stars are compared with those of standard neutron stars (NS).Comment: 5 pages, 2 figures, prepared for the 2nd International Symposium on
Strong Electromagnetic Fields and Neutron Stars (SMFNS2011), Varadero, Cuba,
5-7 May 201
Surface Tension between Kaon Condensate and Normal Nuclear Matter Phase
We calculate for the first time the surface tension and curvature coefficient
of a first order phase transition between two possible phases of cold nuclear
matter, a normal nuclear matter phase in equilibrium with a kaon condensed
phase, at densities a few times the saturation density. We find the surface
tension is proportional to the difference in energy density between the two
phases squared. Furthermore, we show the consequences for the geometrical
structures of the mixed phase region in a neutron star.Comment: 7 pages, 5 figures (Latex
Signal of Quark Deconfinement in the Timing Structure of Pulsar Spin-Down
The conversion of nuclear matter to quark matter in the core of a rotating
neutron star alters its moment of inertia. Hence the epoch over which
conversion takes place will be signaled in the spin-down "signal_prl.tex" 581
lines, 22203 characters characteristics of pulsars. We find that an observable
called the braking index should be easily measurable during the transition
epoch and can have a value far removed (by orders of magnitude) from the
canonical value of three expected for magnetic dipole radiation, and may have
either sign. The duration of the transition epoch is governed by the slow loss
of angular momentum to radiation and is further prolonged by the reduction in
the moment of inertia caused by the phase change which can even introduce an
era of spin-up. We estimate that about one in a hundred pulsars may be passing
through this phase. The phenomenon is analogous to ``bachbending'' observed in
the moment of inertia of rotating nuclei observed in the 1970's, which also
signaled a change in internal structure with changing spin.Comment: 5 pages, 4 figures, Revtex. (May 12, 1997, submitted to PRL
Hyperons in a relativistic mean-field approach to asymmetric nuclear matter
Relativistic mean-field theory with meson, nonlinear isoscalar
self-interactions and isoscalar-isovector cross interaction terms with
parametrizations obtained to reproduce Dirac-Brueckner-Hartree-Fock
calculations for nuclear matter is used to study asymmetric nuclear matter
properties in -equilibrium, including hyperon degrees of freedom and
(hidden) strange mesons. Influence of cross interaction on composition of
hyperon matter and electron chemical potential is examined. Softening of
nuclear equation of state by the cross interactions results in lowering of
hyperonization, although simultaneously enhancing a hyperon-induced decrease of
the electron chemical potential, thus indicating further shift of a kaon
condensate occurence to higher densities.Comment: 11 pages, 7 figures, 3 tables, published in Phys. Rev.
Sensitivity of the Moment of Inertia of Neutron Stars to the Equation of State of Neutron-Rich Matter
The sensitivity of the stellar moment of inertia to the neutron-star matter
equation of state is examined using accurately-calibrated relativistic
mean-field models. We probe this sensitivity by tuning both the density
dependence of the symmetry energy and the high density component of the
equation of state, properties that are at present poorly constrained by
existing laboratory data. Particularly attractive is the study of the fraction
of the moment of inertia contained in the solid crust. Analytic treatments of
the crustal moment of inertia reveal a high sensitivity to the transition
pressure at the core-crust interface. This may suggest the existence of a
strong correlation between the density dependence of the symmetry energy and
the crustal moment of inertia. However, no correlation was found. We conclude
that constraining the density dependence of the symmetry energy - through, for
example, the measurement of the neutron skin thickness in 208Pb - will place no
significant bound on either the transition pressure or the crustal moment of
inertia.Comment: 25 pages, 8 figures, 5 table
Neutron spin polarization in strong magnetic fields
The effects of strong magnetic fields on the inner crust of neutron stars are
investigated after taking into account the anomalous magnetic moments of
nucleons. Energy spectra and wave functions for protons and neutrons in a
uniform magnetic field are provided. The particle spin polarizations and the
yields of protons and neutrons are calculated in a free Fermi gas model.
Obvious spin polarization occurs when G for protons and
G for neutrons, respectively. It is shown that the neutron spin
polarization depends solely on the magnetic field strength.Comment: Replaced by the revised version; 10 pages, including 3 eps figure
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