183 research outputs found
Conversion of neutron stars to strange stars as the central engine of gamma-ray bursts
We study the conversion of a neutron star to a strange star as a possible
energy source for gamma-ray bursts. We use different recent models for the
equation of state of neutron star matter and strange quark matter. We show that
the total amount of energy liberated in the conversion is in the range of (1-4)
10^{53} ergs (one order of magnitude larger than previous estimates) and is in
agreement with the energy required to power gamma-ray burst sources at
cosmological distances.Comment: ApJ, 530, 2000 February 20, Lxxx (in press
On the nature of bimodal initial velocity distribution of neutron stars
We propose that the bimodal nature of the kick velocity distribution of radio
pulsars is connected with the dichotomy between hadronic stars ({\it i.e.}
neutron stars with no quark matter content) and quark stars. Bimodality can
appear due to different mechanisms of explosion which leads to the formation of
two types of compact stars or due to two different sets of parameters mastering
a particular kick mechanism. The low velocity maximum (at km
s) is connected with hadronic star formation, whereas the second peak
corresponds to quark stars. In the model of delayed collapse of hadronic stars
to quark stars (Berezhiani et al. 2003\nocite{bbd2003}) quark deconfinement
leads to a second energy release, and to a second kick, in addition to the kick
imparted to the newly formed hadronic star during the supernova explosion. If
the electromagnetic rocket mechanism can give a significant contribution to
pulsar kicks, then the high velocity peak can be connected with the shorter
initial spin periods of quark stars with respect to hadronic stars. We discuss
{\it pro et contra} of these scenarios.Comment: 8 pages with 2 figures; accepted to A&
Rapidly rotating strange stars for a new equation of state of strange quark matter
For a new equation of state of strange quark matter, we construct equilibrium
sequences of rapidly rotating strange stars in general relativity. The
sequences are the normal and supramassive evolutionary sequences of constant
rest mass. We also calculate equilibrium sequences for a constant value of
corresponding to the most rapidly rotating pulsar PSR 1937 + 21. In
addition to this, we calculate the radius of the marginally stable orbit and
its dependence on , relevant for modeling of kilo-Hertz quasi-periodic
oscillations in X-ray binaries.Comment: Two figures, uses psbox.tex and emulateapj5.st
Probing the isospin dependence of the in-medium nucleon-nucleon cross sections with radioactive beams
Within a transport model we search for potential probes of the isospin
dependence of the in-medium nucleon-nucleon (NN) cross sections. Traditional
measures of the nuclear stopping power are found sensitive to the magnitude but
they are ambiguous for determining the isospin dependence of the in-medium NN
cross sections. It is shown that isospin tracers, such as the neutron/proton
ratio of free nucleons, at backward rapidities/angles in nuclear reactions
induced by radioactive beams in inverse kinematics is a sensitive probe of the
isospin dependence of the in-medium NN cross sections. At forward
rapidities/angles, on the other hand, they are more sensitive to the density
dependence of the symmetry energy. Measurements of the rapidity/angular
dependence of the isospin transport in nuclear reactions will enable a better
understanding of the isospin dependence of in-medium nuclear effective
interactions.Comment: 19 pages including 7 figures, submitted to Phys. Rev.
Effect of symmetry energy on two-nucleon correlation functions in heavy-ion collisions induced by neutron-rich nuclei
Using an isospin-dependent transport model, we study the effects of nuclear
symmetry energy on two-nucleon correlation functions in heavy ion collisions
induced by neutron-rich nuclei. We find that the density dependence of the
nuclear symmetry energy affects significantly the nucleon emission times in
these collisions, leading to larger values of two-nucleon correlation functions
for a symmetry energy that has a stronger density dependence. Two-nucleon
correlation functions are thus useful tools for extracting information about
the nuclear symmetry energy from heavy ion collisions.Comment: Revised version, to appear in Phys. Rev. Let
Chiral model approach to quark matter nucleation in neutron stars
The nucleation process of quark matter in both cold and hot dense hadronic
matter is investigated using a chiral approach to describe the quark phase. We
use the Nambu-Jona-Lasinio and the Chromo Dielectric models to describe the
deconfined phase and the non-linear Walecka model for the hadronic one. The
effect of hyperons on the transition phase between hadronic and quark matter is
studied. The consequences of the nucleation process for neutron star physics
are outlined
Strange Stars with Realistic Quark Vector Interaction and Density-Dependent Scalar Potential
We derive an equation of state (EOS) for strange matter, starting from an interquark potential which (i) has asymptotic freedom built into it, (ii) shows confinement at zero density (rho(B)=0) and deconfinement at high rho(B), and (iii) gives a stable configuration for chargeless, beta-stable quark matter. This EOS is then used to calculate the structure of Strange Stars, and in particular their mass-radius relation. Our present results confirm and reinforce the recent claim [1,2] that the compact objects associated with the X-ray pulsar Her X-1, and with the X-ray burster 4U 1820-30 are strange stars
Quark-hadron phase transition in a neutron star under strong magnetic fields
We study the effect of a strong magnetic field on the properties of neutron
stars with a quark-hadron phase transition. It is shown that the magnetic field
prevents the appearance of a quark phase, enhances the leptonic fraction,
decreases the baryonic density extension of the mixed phase and stiffens the
total equation of state, including both the stellar matter and the magnetic
field contributions. Two parametrisations of a density dependent static
magnetic field, increasing, respectively, fast and slowly with the density and
reaching G in the center of the star, are considered. The
compact stars with strong magnetic fields have maximum mass configurations with
larger masses and radius and smaller quark fractions. The parametrisation of
the magnetic field with density has a strong influence on the star properties.Comment: 15 pages, 6 figures, 8 tables, accepted for publication in J. Phys.
The Microscopic Approach to Nuclear Matter and Neutron Star Matter
We review a variety of theoretical and experimental investigations aimed at
improving our knowledge of the nuclear matter equation of state. Of particular
interest are nuclear matter extreme states in terms of density and/or isospin
asymmetry. The equation of state of matter with unequal concentrations of
protons and neutrons has numerous applications. These include heavy-ion
collisions, the physics of rare, short-lived nuclei and, on a dramatically
different scale, the physics of neutron stars. The "common denominator" among
these (seemingly) very different systems is the symmetry energy, which plays a
crucial role in both the formation of the neutron skin in neutron-rich nuclei
and the radius of a neutron star (a system 18 orders of magnitude larger and 55
orders of magnitude heavier). The details of the density dependence of the
symmetry energy are not yet sufficiently constrained. Throughout this article,
our emphasis will be on the importance of adopting a microscopic approach to
the many-body problem, which we believe to be the one with true predictive
power.Comment: 56 pages, review article to appear in the International Journal of
Modern Physics
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