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1.
We investigate the effect of exotic matter in particular, hyperon matter on neutron star properties such as equation of state
(EoS), mass-radius relationship and bulk viscosity. Here we construct equations of state within the framework of a relativistic
field theoretical model. As hyperons are produced abundantly in dense matter, hyperon–hyperon interaction becomes important
and is included in this model. Hyperon–hyperon interaction gives rise to a softer EoS which results in a smaller maximum mass
neutron star compared with the case without the interaction. Next we compute the coefficient of bulk viscosity and the corresponding
damping time scale due to the non-leptonic weak process including Λ hyperons. Further, we investigate the role of the bulk
viscosity on gravitational radiation driven r-mode instability in a neutron star of given mass and temperature and find that
the instability is effectively suppressed.
相似文献
2.
B. Kmpfer 《Astronomische Nachrichten》1984,305(4):193-197
We derive an upper bound on neutron star masses by using model equations of state in the nuclear matter density region and the causality limited equation of state in the ultradense region. Supposing that the model equations of state describe neutron star matter at nuclear matter density correctly we find as bound 3.75 M⊙. For large fiducial densities one gets a maximum mass which is above a previous estimate. 相似文献
3.
V. M. Lipunov 《Astrophysics and Space Science》1982,82(2):343-361
The general case of non-radial accretion is assumed to occur in real binary systems containing X-ray pulsars. The structure and the stability of the magnetosphere, the interaction between the magnetosphere and accreted matter, as well as evolution of neutron star in close binary system are examined within the framework of the two-stream model of nonradial accretion onto a magnetized neutron star. Observable parameters of X-ray pulsars are explained in terms of the model considered. 相似文献
4.
In our preceding paper we found solutions for the equations of the bimetric scalar—tensor theory of gravitation for neutron
stars, in which the scalar field is constant while the metric tensor satisfies the equations of the general theory of relativity.
In the present paper we find analogous solutions for different versions of the equation of state of the matter of a neutron
star.
Translated from Astrofizika, Vol. 41, No. 2, pp. 297–301. April-June, 1998. 相似文献
5.
S. Campana M. Colpi S. Mereghetti L. Stella M. Tavani 《Astronomy and Astrophysics Review》1998,8(4):279-316
Summary. Soft X–ray Transients (SXRTs) have long been suspected to contain old, weakly magnetic neutron stars that have been spun
up by accretion torques. After reviewing their observational properties, we analyse the different regimes that likely characterise
the neutron stars in these systems across the very large range of mass inflow rates, from the peak of the outbursts to the
quiescent emission. While it is clear that close to the outburst maxima accretion onto the neutron star surface takes place,
as the mass inflow rate decreases, accretion might stop at the magnetospheric boundary because of the centrifugal barrier
provided by the neutron star. For low enough mass inflow rates (and sufficiently short rotation periods), the radio pulsar
mechanism might turn on and sweep the inflowing matter away. The origin of the quiescent emission, observed in a number of
SXRTs at a level of , plays a crucial role in constraining the neutron star magnetic field and spin period. Accretion onto the neutron star surface
is an unlikely mechanism for the quiescent emission of SXRTs, as it requires very low magnetic fields and/or long spin periods.
Thermal radiation from a cooling neutron star surface in between the outbursts can be ruled out as the only cause of the quiescent
emission.
We find that accretion onto the neutron star magnetosphere and shock emission powered by an enshrouded radio pulsar provide
far more plausible models. In the latter case the range of allowed neutron star spin periods and magnetic fields is consistent
with the values recently inferred from the properties of kHz quasi-periodic oscillation in low mass X–ray binaries. If quiescent
SXRTs contain enshrouded radio pulsars, they provide a missing link between X–ray binaries and millisecond pulsars.
Received 4 November 1997; Accepted 15 April 1998 相似文献
6.
In part I we suggested an approximate equation to determine the contribution of relativistic effects to the moment of inertia
of a superdense star. In the present paper it is tested on model neutron stars with nine different variants of the equation
of state of superdense matter. It is established that the approximation error does not exceed 5% for stable configurations.
A more accurate version of the Ravenhall—Pethick equation [D. G. Ravenhall and C. J. Pethick, Astrophys. J., 424, 846 (1994)]
for the moment of inertia as a function of the mass and radius of a neutron star is derived.
Translated from Astrofizika, Vol. 40, No. 4, pp. 507–516, October–December, 1997. 相似文献
7.
D. M. Sedrakian 《Astrophysics》2006,49(1):83-87
The electromagnetic properties of neutron stars (pulsars) are studied. It is shown that taking the presence of two angular
rotation velocities of the components of neutron stars and the first corrections to the general theory of relativity into
account in the equations of hydrodynamic equilibrium for the plasma and in Maxwell’s equations leads to the generation of
toroidal magnetic fields in the depths of a neutron star.
__________
Translated from Astrofizika, Vol. 49, No. 1, pp. 97–101 (February 2006). 相似文献
8.
The Ginzburg-Landau equations are derived for the magnetic and gluomagnetic gauge fields in the color superconducting core
of a neutron star containing a CFL-condensate of diquarks. The interaction of the diquark CFL-condensate with the magnetic
and gluomagnetic gauge fields is taken into account. The behavior of the magnetic field in a neutron star is studied by solving
the Ginzburg-Landau equations taking correct account of the boundary conditions, including the gluon confinement conditions.
The magnetic field distribution in the quark and hadronic phases of a neutron star is found. It is shown that a magnetic field
generated in the hadronic phase by the entrainment effect penetrates into the quark core in the form of quark vortex filaments
because of the presence of screening Meissner currents.
__________
Translated from Astrofizika, Vol. 50, No. 1, pp. 87–98 (February 2007). 相似文献
9.
The gravitational radiation from millisecond pulsars owing to glitches in their angular velocity is examined. It is assumed
that the energy transferred from interior superfluid regions to the crust of a neutron star is converted into gravitational
wave energy by damping oscillations of the matter in the star. The gravitational wave intensity and amplitude are calculated
for fourteen millisecond pulsars. Gravitational radiation can explain the observed spin-down of millisecond pulsars and an
estimate is given for the magnetic field at which the proposed mechanism predominates in the spin-down of these pulsars.
__________
Translated from Astrofizika, Vol. 51, No. 3, pp. 479–486 (August 2008). 相似文献
10.
L.W. Kebede 《Astrophysics and Space Science》2002,282(1):131-140
Plasma density gradient which is inherent to degenerate neutron star matter is shown to lead to large scale plasma diffusion
and subsequent charge separation. The surface (internal) fields generated by the spinning separated charges are found to be
dipolar with intensities of ≃ 1014 G (for the surface fields) very early in the life-time of a typical neutron star. The internal fields, on the other hand,
are relatively much weaker. These fields, which in this case are also shown to be temperature dependent, decay as a result
of neutrino and photon emissions. The decay law derived from equations of standard cooling calculations and the equation connecting
the magnetic field and temperature is indicated to have two distinct modes, each corresponding to the two branches of a typical
neutron star cooling curve. We have found that results derived from the decay law are consistent with observational findings.
Based on the theory behind our new model, we have also argued to show that isolated millisecond and sub-millisecond pulsars
might be very rare objects.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
James M. Lattimer 《Astrophysics and Space Science》2007,308(1-4):371-379
Recent measurements of thermal radiation from neutron stars have suggested a rather broad range of radiation radii (
). Sources in M13 and Omega Cen imply R
∞∼12–14 km, but X7 in 47 Tuc implies R
∞∼16–20 km and RX J1856-3754 R
∞>17 km. If these measurements are all correct, only a limited selection of EOS’s could be consistent with them, but a broad
range of neutron star masses (up to 2 M⊙) would also be necessary. The surviving equations of state are incompatible with significant softening above nuclear saturation
densities, such as would occur with Boson condensates, a low-density quark-hadron transition, or hyperons. Other potential
constraints, such as from QPO’s, radio pulsar mass and moment of inertia measurements, and neutron star cooling, are compared.
US DOE Grant DE-FG02-87ER-40317. 相似文献
12.
Natural, low-frequency, hydromagnetic oscillations of an isolated, nonrotating neutron star, which are localized in the peripheral
crust, the structure of which is determined by the electron-nuclear plasma (the Ae phase), are studied. The plasma medium
of the outer crust is treated as a homogeneous, infinitely conducting, incompressible continuum, the motions of which are
determined by the equations of magnetohydrodynamics. In the approximation of a constant magnetic field inside the crust (the
magnetic field outside the star is assumed to have a dipole structure), the spectrum of normal poloidal and toroidal hydromagnetic
oscillations, due to presumed residual fluctuations of flow and their associated fluctuations in magnetic field strength,
is calculated. Numerical estimates given for the periods of MHD oscillations fall in the range of periods of radio pulsar
emission, indicating a close connection between the residual hydromagnetic oscillations and the electromagnetic activity of
neutron stars.
Translated from Astrofizika, Vol. 40, No. 1, pp. 77–86, January–March, 1997. 相似文献
13.
V934 Her is a detached system, consisting of a cool giant and a neutron star. The neutron star accretes matter fromthe stellarwind
of the giant.Multicolor photoelectric observationsmade in 1997–2011 revealed a 415-day period, close to that, discovered spectroscopically
from radial velocities. This period is considered to be the orbital period of orbital motion of the neutron star around the
red giant. The wave with this period in the U-band has the largest amplitude 0m.12. We also detected multiperiodic pulsations of the red giant. The light curve in the V -band is dominated by a pulsation wave with the period of 28.82 days and the amplitude of 0m.10. 相似文献
14.
Edward P. J. Van den Heuvel 《Journal of Astrophysics and Astronomy》1984,5(3):209-233
The peculiar combination of a relatively short pulse period and a relatively weak surface dipole magnetic field strength of
binary radio pulsars finds a consistent explanation in terms of (i) decay of the surface dipole component of neutron-star
magnetic fields on a timescale of (2–5) × 106 yr, in combination with (ii) spin-up of the rotation of the neutron star during a subsequent mass-transfer phase.
The four known binary radio pulsars appear to fall into two different categories. Two of them, PSR 0655 + 64 and PSR 1913
+ 16, have short orbital periods (<25 h) and high mass functions, indicating companion masses 0.7M⊙ (∼1 (± 0.3) M⊙ and 1.4 M⊙, respectively). The other two, PSR 0820 + 02 and PSR 1953 + 29, have long orbital periods (117d),
nearly circular orbits, and low, almost identical mass functions of about 3×10-3 M⊙, suggesting companion masses of about 0.3M⊙. It is pointed out that these two classes of systems are expected to be formed by the later evolution of binaries consisting
of a neutron star and a normal companion star, in which the companion was (considerably) more massive than the neutron star,
or less massive than the neutron star, respectively. In the first case the companion of the neutron star in the final system
will be a massive white dwarf, in a circular orbit, or a neutron star in an eccentric orbit. In the second case the final
companion to the neutron star will be a low-mass (∼ 0.3 M⊙) helium white dwarf in a wide and nearly circular orbit.
In systems of the second type the neutron star was most probably formed by the accretion-induced collapse of a white dwarf.
This explains in a natural way why PSR 1953 + 29 has a millisecond rotation period and PSR 0820 + 02 has not.
Among the binary models proposed for the formation of the 1.5-millisecond pulsar, the only ones that appear to be viable are
those in which the companion disappeared by coalescence with the neutron star. In such models the companion may have been
a red dwarf of mass 0.03M⊙, a neutron star, or a massive (>0.7M⊙) white dwarf. Only in the last-mentioned case is a position of the pulsar close to the galactic plane a natural consequence.
In the first-mentioned case the progenitor system most probably was a cataclysmic-variable binary in which the white dwarf
collapsed by accretion. 相似文献
15.
The dynamics of the vortex lattice in the inner crust of a neutron star is considered. A general equation of motion is obtained
and solved under the assumption that there are regions of pinned and of free vortices. By comparing these solutions with observational
data for the Vela pulsar, the relative moments of inertia of regions of relaxation with the corresponding characteristic times
are calculated for two model stars with different equations of state. It is shown that the theory can be reconciled with observations
of the relaxation of pulsar angular velocity only for model stars with extremely stiff equations of state.
Translated from Astrofizika, Vol. 40, No. 1, pp. 67–76, January–March, 1997. 相似文献
16.
The dynamics of the rotation of a two-component system in the core of a neutron star is analyzed within the framework of the
generai theory of relativity (GTR). A theory of the relaxation of the angular velocity of the Vela pulsar is developed with
allowance for GTR corrections. From a comparison of the theory with observational data on the Vela pulsar, the relative moments
and positions of the relaxation regions are found for one of the standard models of a neutron star. It is shown that the theory
agrees with observations and supports this model neutron star as an acceptable pulsar model.
Translated from Astrofizika, Vol. 43, No. 1, pp. 85-94, January–March, 2000. 相似文献
17.
Pranab Ghosh 《Journal of Astrophysics and Astronomy》1995,16(2):289-305
I review our understanding of the evolution of the spin periods of neutron stars in binary stellar systems, from their birth
as fast, spin-powered pulsars, through their middle life as accretion-powered pulsars, upto their recycling or “rebirth” as
spin-powered pulsars with relatively low magnetic fields and fast rotation. I discuss how the new-born neutron star is spun
down by electromagnetic and “propeller” torques, until accretion of matter from the companion star begins, and the neutron
star becomes an accretion-powered X-ray pulsar. Detailed observations of massive radio pulsar binaries like PSR 1259-63 will
yield valuable information about this phase of initial spindown. I indicate how the spin of the neutron star then evolves
under accretion torques during the subsequent phase as an accretion-powered pulsar. Finally, I describe how the neutron star
is spun up to short periods again during the subsequent phase of recycling, with the accompanying reduction in the stellar
magnetic field, the origins of which are still not completely understood. 相似文献
18.
The dynamics of the rotation of a two-component system in a neutron star is considered within the framework of the general
theory of relativity. Equations for the angular velocities of the normal and superfluid components are obtained in the W approximation.
It is shown that the solutions of these equations can describe the relaxation of pulsar angular velocity after a glitch.
Translated from Astrofizika, Vol. 42, No. 1, pp. 89–100, January–March, 1999. 相似文献
19.
The superconducting proton condensate in the “npe” phase of a neutron star is considered. It is shown to be a type II superconductor
in the outer layer of the “npe” phase and a type I superconductor in the inner layer. Relaxation times are found for elastic
scattering of normal relativistic electrons from the magnetic fields of proton vortex clusters in the case of a type II superconductor
and elastic scattering from the magnetic field at the center of a neutron vortex in the case of a superconductor of the first
kind. The dynamical relaxation times obtained for the angular velocity of the pulsar PSR 0833—45 vary, as a function of the
density of the layers taking part in the relaxation process, within a fairly wide range: from several hours to l09 years. This means that the characteristic times of variation of pulsar angular velocity may be observed to lie in the indicated
time range.
Translated from Astrofizika, Vol. 40, No. 4, op. 497–506, October–December, 1997. 相似文献
20.
We report the results of spectropolarimetric observations of the supergiant ζ Ori A made with 6-m BTA telescope of the SAO RAS. We found regular variations of line profiles in the spectrum of the star
with a period of 1–3 hours and point to their possible association with nonradial photospheric pulsations. We also searched
for a possible weak magnetic field in ζ Ori A, but observations did not confirm the existence of such a field in the star considered. 相似文献