738 research outputs found
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
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
First Order Kaon Condensate
First order Bose condensation in asymmetric nuclear matter and in neutron
stars is studied, with particular reference to kaon condensation. We
demonstrate explicitly why the Maxwell construction fails to assure equilibrium
in multicomponent substances. Gibbs conditions and conservation laws require
that for phase equilibrium, the charge density must have opposite sign in the
two phases of isospin asymmetric nuclear matter. The mixed phase will therefore
form a Coulomb lattice with the rare phase occupying lattice sites in the
dominant phase. Moreover, the kaon condensed phase differs from the normal
phase, not by the mere presence of kaons in the first, but also by a difference
in the nucleon effective masses. The mixed phase region, which occupies a large
radial extent amounting to some kilometers in our model neutron stars, is thus
highly heterogeneous. It should be particularly interesting in connection with
the pulsar glitch phenomenon as well as transport properties.Comment: 25 pagees, 20 figures, Late
Kaon Condensation and Dynamical Nucleons in Neutron Stars
We discuss the nature of the kaon condensation phase transition. We find
several features which, if kaons condense in neutron stars, are not only
remarkable, but must surely effect such properties as superfluidity and
transport properties, which in turn are relevant to the glitch phenomenon and
cooling rates of neutron stars. The mixed phase, because of the extensive
pressure range that it spans, will occupy a broad radial extent in a neutron
star. This region is permeated with microscopic drops (and other
configurations) located at lattice sites of one phase immersed in the
background of the other phase. The electric charge on drops is opposite to that
of the background phase {\sl and} nucleons have a mass approximately a factor
two different depending on whether they are in the drops or the background
phase. A large part of the stellar interior has this highly non-homogeneous
structure.Comment: 5 pages, 6 figures, revtex. Physical Review Letters (accepted
Mixed Phase in Compact Starts : M-R relations and radial oscillations
It is believed that quark stars or neutron stars with mixed phase in the core
have smaller radii compared to ordinary compact stars. With the recent
observation of several low radius objects, typically a radius of for
star of mass in low mass X-ray binaries (LMXB), it has become very
important to understand the nature of these objects. An accurate determination
of mass-radius relationship of these objects provide us with a physical
laboratory to study the composition of high density matter and the nature of
phase transition. We study the effect of quark and nuclear matter mixed phase
on mass radius relationship and radial oscillations of neutron stars. We find
that the effect of the mixed phase is to decrease the maximum mass of a stable
neutron star and to decrease the radial frequencies .Comment: guest contribution at Int. Workshop on Astronomy & Relativistic
Astrophysics (IWARA 03)held at Olinda-PE (Brazil) from Oct. 12-17,200
Alien Registration- Glendenning, Elizabeth B. (Portland, Cumberland County)
https://digitalmaine.com/alien_docs/24190/thumbnail.jp
Alien Registration- Glendenning, Lillian B. (Portland, Cumberland County)
https://digitalmaine.com/alien_docs/24192/thumbnail.jp
Stable configurations of hybrid stars with colour-flavour-locked core
We construct static and mass-shedding limit sequences of hybrid stars,
composed of colour flavour locked (CFL) quark matter core, for a set of
equations of state (EOSs). The EOS for the hadronic matter is obtained using
appropriately calibrated extended field theoretical based relativistic
mean-field model. The MIT bag model is employed to compute the EOSs of the CFL
quark matter for different values of the CFL gap parameter in the range of with the deconfinement phase transition density ranging from
(). We find, depending on the
values of the CFL gap parameter and the deconfinement phase transition density,
the sequences of stable configurations of hybrid stars either form third
families of the compact stars or bifurcate from the hadronic sequence. The
hybrid stars have masses with radii km. The
maximum values of mass shedding limit frequency for such hybrid stars are kHz. For the smaller values of the CFL gap parameter and the deconfinement
phase transition density, mass-radius relationships are in harmony with those
deduced by applying improved hydrogen atmosphere model to fit the high quality
spectra from compact star X7 in the globular cluster 47 Tucanae. We observed
for some cases that the third family of compact stars exist in the static
sequence, but, disappear from the mass-shedding limit sequence. Our
investigation suggests that the third family of compact stars in the
mass-shedding limit sequence is more likely to appear, provided they have
maximum mass in the static limit higher than their second family counterpart
composed of pure hadronic matter.Comment: 27 pages including 10 figures. Accepted in Phys. Rev.
First Order Kaon Condensation in Neutron Stars: Finite Size Effects in the Mixed Phase
We study the role of Coulomb and surface effects on the phase transition from
dense nuclear matter to a mixed phase of nuclear and kaon-condensed matter. We
calculate corrections to the bulk calculation of the equation of state (EOS)
and the critical density for the transition by solving explicitly for
spherical, cylindrical, and planar structures. The importance of Debye
screening in the determination of the charged particle profiles is studied in
some detail. We find that the surface and Coulomb contributions to the energy
density are small, but that they play an important role in the determination of
the critical pressure for the transition, as well as affecting the size and
geometry of favored structures. This changes the EOS over a wide range of
pressure and consequently increases the maximum mass by about 0.1 solar masses.
Implications for transport properties of the mixed phase are also discussed.Comment: 18 pages, 6 figure
Kaon condensation in the quark-meson coupling model and compact stars
The properties of neutron stars constituted of a crust of hadrons and an
internal part of hadrons and kaon condensate are calculated within the
quark-meson-coupling model. We have considered stars with nucleons only in the
hadron phase and also stars with hyperons as well. The results are compared
with the ones obtained from the non-linear Walecka model for the hadronic
phase.Comment: 10 pages, 6 figure
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