共查询到20条相似文献，搜索用时 15 毫秒
1.
Michelle B. Larson † Bennett Link 《Monthly notices of the Royal Astronomical Society》2002,333(3):613-622
Many radio pulsars exhibit glitches wherein the star's spin rate increases fractionally by ∼10−10 –10−6 . Glitches are ascribed to variable coupling between the neutron star crust and its superfluid interior. With the aim of distinguishing among different theoretical explanations for the glitch phenomenon, we study the response of a neutron star to two types of perturbations to the vortex array that exists in the superfluid interior: (1) thermal motion of vortices pinned to inner crust nuclei, initiated by sudden heating of the crust, (e.g., a starquake), and (2) mechanical motion of vortices (e.g., from crust cracking by superfluid stresses). Both mechanisms produce acceptable fits to glitch observations in four pulsars, with the exception of the 1989 glitch in the Crab pulsar, which is best fitted by the thermal excitation model. The two models make different predictions for the generation of internal heat and subsequent enhancement of surface emission. The mechanical glitch model predicts a negligible temperature increase. For a pure and highly conductive crust, the thermal glitch model predicts a surface temperature increase of as much as ∼2 per cent, occurring several weeks after the glitch. If the thermal conductivity of the crust is lowered by a high concentration of impurities, however, the surface temperature increases by ∼10 per cent about a decade after a thermal glitch. A thermal glitch in an impure crust is consistent with the surface emission limits following the 2000 January glitch in the Vela pulsar. Future surface emission measurements coordinated with radio observations will constrain glitch mechanisms and the conductivity of the crust. 相似文献
2.
P. B. Jones 《Monthly notices of the Royal Astronomical Society》2006,371(3):1327-1333
Neutron star inner cores with several charged baryonic components are likely to be analogues of the two-gap superconductor which is of current interest in condensed-matter physics. Consequently, type I superconductivity is less probable than type II but may nevertheless be present in some intervals of matter density. The intermediate-state structure formed at finite magnetic flux densities after the superconducting transitions is subject to buoyancy, frictional and neutron vortex interaction forces. These are estimated and it is shown that the most important frictional force is that produced by the stable stratification of neutron star matter, the irreversible process being diffusion in the normal, finite magnetic flux density, parts of the structure. The length-scale of the structure, in directions perpendicular to the local magnetic field is of crucial importance. For small scales, the flux comoves with the neutron vortices, as do the proton vortices of a type II superconductor. But for much larger length-scales, flux movement tends to that expected for normal charged Fermi systems. 相似文献
3.
Armen Sedrakian James M. Cordes 《Monthly notices of the Royal Astronomical Society》1999,307(2):365-375
We show that the crust–core interface in neutron stars acts as a potential barrier to the peripheral neutron vortices approaching the interface in the model in which these are coupled to the proton vortex clusters. This elementary barrier arises because of the interaction of vortex magnetic flux with the Meissner currents set up by the crustal magnetic field at the interface. The dominant part of the force is derived from the cluster–interface interaction. As a result of the stopping of the continuous neutron vortex current through the interface, angular momentum is stored in the superfluid layers in the vicinity of the crust–core interface during the interglitch period. Discontinuous annihilation of proton vortices at the boundary restores the neutron vortex current and spins up the observable crust on short time-scales, leading to a glitch in the spin characteristics of a pulsar. 相似文献
4.
The forces acting on the solid crust of a differentially rotating neutron star are examined when a nonuniform excess of chemical
potential exists. The resultant of the external forces, a stress force, is expressed in terms of a centrifugal buoyancy force
and the deformation of the star’s crust under the action of this force is calculated. It is shown that there is a region within
the star where the resulting stresses lead to fracture of the crust when the difference in the angular velocities of the superfluid
and normal components reaches a critical value. The “centrifugal buoyancy” mechanism for generating a glitch is used to estimate
the parameters of glitches in the Vela pulsar.
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Translated from Astrofizika, Vol. 50, No. 2, pp. 183–197 (May 2007). 相似文献
5.
N. Andersson T. Sidery G. L. Comer 《Monthly notices of the Royal Astronomical Society》2006,368(1):162-170
We discuss vortex-mediated mutual friction in the two-fluid model for superfluid neutron star cores. Our discussion is based on the general formalism developed by Carter and collaborators, which makes due distinction between transport velocity and momentum for each fluid. This is essential for an implementation of the so-called entrainment effect, whereby the flow of one fluid imparts momentum in the other and vice versa. The mutual friction follows by balancing the Magnus effect that acts on the quantized neutron vortices with resistivity due to the scattering of electrons off of the magnetic field with which each vortex core is endowed. We derive the form of the macroscopic mutual friction force which is relevant for a model based on smooth-averaging over a collection of vortices. We discuss the coefficients that enter the expression for this force, and the time-scale on which the two interpenetrating fluids in a neutron star core are coupled. This discussion confirms that our new formulation accords well with previous work in this area. 相似文献
6.
D. M. Sedrakian 《Astrophysics》2000,43(3):275-281
The influence of the effect of entrainment of superconducting protons by superfluid neutrons on the distribution of neutron
vortices in a rotating neutron star is investigated. It is shown that the proton vortex clusters generated by entrainment
currents create the magnetic structure of a neutron vortex. The average magnetic field induction in a neutron vortex is calculated.
The presence of the magnetic field of a neutron vortex considerably alters the radius of the vortex zone. The width of the
vortex-free zone at the surface of the neutron star’s core increases, reaching macroscopic values on the order of several
meters. This result considerably changes earlier concepts of the distribution of neutron vortices in a neutron star.
Translated from Astrofizika, Vol. 43, No. 3, pp. 377-386, July–September, 2000. 相似文献
7.
K. Glampedakis N. Andersson D. I. Jones 《Monthly notices of the Royal Astronomical Society》2009,394(4):1908-1924
We discuss short wavelength (inertial wave) instabilities present in the standard two-fluid neutron star model when there is sufficient relative flow along the superfluid neutron vortex array. We demonstrate that these instabilities may be triggered in precessing neutron stars, since the angular velocity vectors of the neutron and proton fluids are misaligned during precession. Our results suggest that the standard (Eulerian) slow precession that results for weak drag between the vortices and the charged fluid (protons and electrons) is not seriously affected by the instability. In contrast, the fast precession, which results when vortices are strongly coupled to the charged component, is generally unstable. The presence of this instability renders the standard (solid body) rotation model for free precession inconsistent and makes unsafe conclusions that have recently been drawn regarding neutron star interiors based on observations of precession in radio pulsars. 相似文献
8.
We present a model of a freely precessing neutron star, which is then compared against pulsar observations. The aim is to draw conclusions regarding the structure of the star, and to test theoretical ideas of crust–core coupling and superfluidity. We argue that, on theoretical grounds, it is likely that the core neutron superfluid does not participate in the free precession of the crust. We apply our model to the handful of proposed observations of free precession that have appeared in the literature. Assuming crust-only precession, we find that all but one of the observations are consistent with there being no pinned crustal superfluid at all; the maximum amount of pinned superfluid consistent with the observations is about 10−10 of the total stellar moment of inertia. However, the observations do not rule out the possibility that the crust and neutron superfluid core precess as a single unit. In this case the maximum amount of pinned superfluid consistent with the observations is about 10−8 of the total stellar moment of inertia. Both of these values are many orders of magnitude less than the 10−2 value predicted by many theories of pulsar glitches. We conclude that superfluid pinning, at least as it affects free precession, needs to be reconsidered. 相似文献
9.
Dipankar Bhattacharya 《Journal of Astrophysics and Astronomy》1995,16(2):217-232
Observational evidence, and theoretical models of the magnetic field evolution of neutron stars is discussed. Observational
data indicates that the magnetic field of a neutron star decays significantly only if it has been a member of a close interacting
binary. Theoretically, the magnetic field evolution has been related to the processing of a neutron star in a binary system
through the spin evolution of the neutron star, and also through the accretion of matter on the neutron star surface. I describe
two specific models, one in which magnetic flux is expelled from the superconducting core during spin-down, via a copuling
between Abrikosov fluxoids and Onsager-Feynman vortices; and another in which the compression and heating of the stellar crust
by the accreted mass drastically reduces the ohmic decay time scale of a magnetic field configuration confined entirely to
the crust. General remarks about the behaviour of the crustal field under ohmic diffusion are also made. 相似文献
10.
A recent laboratory experiment suggests that a Kelvin–Helmholtz (KH) instability at the interface between two superfluids – one rotating and anisotropic, the other stationary and isotropic – may trigger sudden spin-up of the stationary superfluid. This result suggests that a KH instability at the crust–core ( 1 S0 –3 P2 –superfluid) boundary of a neutron star may provide a trigger mechanism for pulsar glitches. We calculate the dispersion relation of the KH instability involving two different superfluids including the normal fluid components and their effects on stability, particularly entropy transport. We show that an entropy difference between the core and crust superfluids reduces the threshold differential shear velocity and threshold crust–core density ratio. We evaluate the wavelength of maximum growth of the instability for neutron star parameters and find the resultant circulation transfer to be within the range observed in pulsar glitches. 相似文献
11.
A. N. Timokhin 《Astrophysics and Space Science》2007,308(1-4):345-351
Pulsar “standard model”, that considers a pulsar as a rotating magnetized conducting sphere surrounded by plasma, is generalized
to the case of oscillating star. We developed an algorithm for calculation of the Goldreich-Julian charge density for this
case. We consider distortion of the accelerating zone in the polar cap of pulsar by neutron star oscillations. It is shown
that for oscillation modes with high harmonic numbers (l,m) changes in the Goldreich-Julian charge density caused by pulsations of neutron star could lead to significant altering of
an accelerating electric field in the polar cap of pulsar. In the moderately optimistic scenario, that assumes excitation
of the neutron star oscillations by glitches, it could be possible to detect altering of the pulsar radioemission due to modulation
of the accelerating field.
This work was partially supported by RFBR grant 04-02-16720, and by the grants N.Sh.-5218.2006.2 and RNP-2.1.1.5940. 相似文献
12.
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.
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Translated from Astrofizika, Vol. 51, No. 3, pp. 479–486 (August 2008). 相似文献
13.
A. G. Lyne S. L. Shemar F. Graham Smith 《Monthly notices of the Royal Astronomical Society》2000,315(3):534-542
Shemar & Lyne have previously presented observations and an analysis of 32 glitches and their subsequent relaxations observed in a total of 15 pulsars. These data are brought together in this paper with those published by other authors. We show quantitatively how glitch activity decreases linearly with decreasing rate of slow-down. As indicated previously from studies of the Vela pulsar, the analysis suggests that 1.7 per cent of the moment of inertia of a typical neutron star is normally contained in pinned superfluid which releases its excess angular momentum at the time of a glitch. There is a broad range of glitch amplitude and there is a strong indication that pulsars with large magnetic fields suffer many small glitches while others show a smaller number of large glitches. Transient effects following glitches are very marked in young pulsars and decrease linearly with decreasing rate of slow-down, suggesting that the amount of loosely pinned superfluid decreases with age. We suggest that the low braking index of the Vela and Crab pulsars cannot be caused by a decreasing moment of inertia and should be attributed to step increases in the effective magnetic moment of the neutron star at the glitches. 相似文献
14.
P. B. Jones 《Monthly notices of the Royal Astronomical Society》2009,397(2):1027-1031
The quantum phenomenon of spectral flow which has been observed in laboratory superfluids, such as 3 He-B, controls the drift velocity of proton type II superconductor vortices in the liquid core of a neutron star and so determines the rate at which magnetic flux can be expelled from the core to the crust. In the earliest and most active phases of the anomalous X-ray pulsars and soft-gamma repeaters, the rates are low and consistent with a large fraction of the active crustal flux not linking the core. If normal neutrons are present in an appreciable core matter-density interval, the spectral flow force limits flux expulsion in cases of rapid spin-down, such as in the Crab pulsar or in the propeller phase of binary systems. 相似文献
15.
David Langlois David M. Sedrakian & Brandon Carter 《Monthly notices of the Royal Astronomical Society》1998,297(4):1189-1201
It is shown how to set up a mathematically elegant and fully relativistic superfluid model that can provide a realistic approximation (neglecting small anisotropies due to crust solidity, magnetic fields, etc., but allowing for the regions with vortex pinning) of the global structure of a rotating neutron star, in terms of just two independently moving constituents. One of these represents the differentially rotating neutron superfluid, while the other part represents the combination of all the other ingredients, including the degenerate electrons, the superfluid protons in the core, and the ions in the crust, the electromagnetic interactions of which will tend to keep them locked together in a state of approximately rigid rotation. Order of magnitude estimates are provided for relevant parameters such as the resistive drag coefficient. 相似文献
16.
The theory of the relaxation of pulsar angular velocity is compared with observational data for the first eight glitches of the Vela pulsar. Solutions of the inverse problem in relaxation theory are obtained in the regions of exponential and linear relaxation in the core of the neutron star. From these solutions, a distribution of vortices is found that results in the observed relaxation of the pulsar's angular velocity. It is shown that the pinning of neutron vortices plays the primary role in the region of exponential relaxation, while in the region of linear relaxation one must allow for the variation of the angular velocity of the superfluid component. 相似文献
17.
The nonstationary dynamics of vortices in conventional type II superconductors and in neutron stars is examined in the Newtonian
approximation. A relaxation equation is obtained for vortices approaching an equilibrium distribution after a change in an
external magnetic field. The relaxation times are estimated for vortices in low-temperature superconductors and for proton
vortices in the superconducting core of a neutron star. It is shown that the proton vortex system created by entrainment currents
is rigidly coupled to the neutron vortices.
Translated from Astrofizika, Vol. 52, No. 2, pp. 291–300 (May 2009). 相似文献
18.
In this paper we model the gravitational wave emission of a freely precessing neutron star. The aim is to estimate likely source strengths, as a guide for gravitational wave astronomers searching for such signals. We model the star as a partly elastic, partly fluid body with quadrupolar deformations of its moment of inertia tensor. The angular amplitude of the free precession is limited by the finite breaking strain of the star's crust. The effect of internal dissipation on the star is important, with the precession angle being rapidly damped in the case of a star with an oblate deformation. We then go on to study detailed scenarios where free precession is created and/or maintained by some astrophysical mechanism. We consider the effects of accretion torques, electromagnetic torques, glitches and stellar encounters. We find that the mechanisms considered are either too weak to lead to a signal detectable by an Advanced LIGO interferometer, or occur too infrequently to give a reasonable event rate. We therefore conclude that, using our stellar model at least, free precession is not a good candidate for detection by the forthcoming laser interferometers. 相似文献
19.
The superfluid core (“npe” phase) of a neutron star, consisting of superfluid neutrons, superconducting protons, and normal
electrons, is considered. The Gibbs thermodynamic potential of a superconducting proton vortex in a proton superconductor
of the second kind, interacting with the normal core of a neutron vortex of radius r ≪ λ parallel to it (λ is the depth of
penetration), is calculated. It is shown that under this assumption, the capture by the core of only one vortex turns out
to be energetically favored. The force exerted on the proton vortex by the entrainment current, always directed toward the
core, is found. The corresponding force for a proton antivortex is directed outward toward the outer boundary of the neutron
vortex. It is shown that the fluctuational formation of a vortex-antivortex pair is possible at a large distance from the
core under the action of the entrainment current. Under the action of the entrainment current, the antivortex travels outward,
while the vortex remains inside the neutron vortex. It is shown that the formation of new proton vortices is possible only
in the region in which the entrainment magnetic field strength is H(ρ) > Hcl (Hcl is the first critical field).
Translated from Astrofizika, Vol. 42, No. 2, pp. 225–234, April–June, 1999 相似文献
20.
There is a 3P2 neutron superfluid region in NS (neutron star) interior. For a rotating NS the 3P2 superfluid region is like a system of rotating magnetic dipoles. It will give out electromagnetic radiation, which may provide a new heating mechanism of NSs. This mechanism plus some cooling agent may give a sound explanation to NS glitches. 相似文献