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1.
A. D. Sedrakian 《Astrophysics and Space Science》1996,236(2):267-276
The phonon excitation spectrum of Coulomb lattice in the neutron star crusts is studied by solving Dyson's equation for phonons. It is shown that a strong renormalization of the phonon spectrum occurs at densities
s
/4 for the crustal matter compositions with spherical nuclei, which imply relatively small nuclear mass numbers and charges. It is shown that, the lattice becomes unstable against density fluctuations above a critical density of the order of
s
/3, where
s
2.6x1014 g cm–3 is the nuclear saturation density. The neutron quasiparticle spectrum and the virtual mass of a nucleus are briefly discussed. 相似文献
2.
A model of a first generation intermediate star of 5M
, with Z=0 has been considered. The model is at an advanced stage of its evolution and has a double shell burning. It burns helium in the inner shell, and hydrogen, via CNO cycle, in the outer shell.
=(log/log)
T
and
T
=(log/logT)
were computed allowing for the oscillations of the relative mass abundance of the reagents in nuclear reactions. Including
=(log/log)
T
and
=(log/logT)
of mean molecular weight and the effect of the oscillations of abundances due to nuclear reactions, stability was studied. Contrary to the results of the static calculations, we found that instability due to the excitation mechanism provided by the high temperature sensitivity of energy generation rate propagates up to the surface. Thus the model in question was found to be unstable against radial adiabatic pulsations, in its fundamental mode. 相似文献
3.
General theory of electrical conductivity of a multicomponent mixture of degenerate fermions in a magnetic fieldB, developed in the preceding article (this volume), is applied to a matter in neutron star interiors at densities 0, where 0 = 2.8×1014 g cm–3 is the standard nuclear matter density. A model of free-particle mixture ofn, p, e is used, with account for appearance of –-hyperons at >
c
, where
c
40. The electric resistivities along and acrossB, and , and the Hall resistivity
H
are calculated and fitted by simple analytical formulae at
c
and >
c
for the cases of normal or superfluid neutrons provided other particles are normal. Charge transport alongB is produced by electrons, due to their Coulombic collisions with other charged particles; is independent ofB and almost independent of the neutron superfluidity. Charge transport acrossB at largeB may be essentially determined by other charged particles. If
c
, one has = [1 + (B/B
0)2] for the normal neutrons, and for the superfluid neutrons, while
H
=
B/B
e
for both cases. HereB
e
109
T
8
2
G,B
01011
T
8
2
G, andT
8 is temperature in units of 108 K. Accordingly for the normal neutrons atBB
0, the transverse resistivity suffers an enhancement, 1/4 1. When 50 andB varies from 0 toBB
p
1013
T
8
2
G, increases by a factor of about 103–104 and
H
changes sign. WhenBB
p
, remains constant for the superfluid neutrons, and
H
B
2 for the normal neutrons, while
H
B for any neutron state. Strong dependence of resistivity onB, T, and may affect evolution of magnetic fields in neutron star cores. In particular, the enhancement of at highB may noticeably speed up the Ohmic decay of those electric currents which are perpendicular toB. 相似文献
4.
Low-mass strange stars with a crust are investigated within the framework of the bag model. The crust, which consists of degenerate electrons and atomic nuclei, has a limiting boundary density
cr
, which is determined by the mass of the crust, and it cannot exceed the value
drip
= 4.3·1011 g/cm3, corresponding to the density at which neutrons drip from nuclei. For different values of
cr
in the low-mass range (M 0.1 M) we calculate several series of configurations: we find the dependence of the stellar mass M on the central density
c
for
cr
= const, with 109 g/cm3
cr
drip
, and for each series we determine the parameters of the configuration for which the condition dM/d
c
> 0 is violated. When the boundary density of the crust decreases to 109 g/cm3, the minimum mass of a strange star decreases to M
min 10-3 M, while the radius reaches 600 km. 相似文献
5.
For the region after the recombination era of the Universe the hydrodynamical density waves are analyzed including shear viscosity and heat conduction for =c as well as for <c(c is the critical density of the Universe). Very near to the end of the recombination era (z=1200) we find the well-known Jeans instability. It is shown that the influence of the shear viscosity on the instabilities in negligible, however, a visible influence of the bulk viscosity is present. 相似文献
6.
M. A. Eritsian 《Astrophysics》2004,47(3):305-312
Of the 7500 stars cited in the Catalog of starlight polarization, those which satisfy the condition P
obs % and A
V 0m.5 are selected. It is presumed that the selected stars (n=216) have circularly polarized light. 相似文献
7.
Chisnell-Chester-Whitham method has been used to study the propagation of diverging hydromagnetic cylindrical shock through an infinitely electrically conducting self-gravitating gas having an initial density distribution 0= r-w where is the density at the axis of symmetry andw is a constant, simultaneously for the two cases, viz.: (i) when the shock is weak and (ii) when it is strong. The magnetic field is taken to be axial and initially of constant strength. Analytical relations for shock velocity and shock strength have been obtained. the expressions for the pressure, the density and the particle velocity immediately behind the shock have also been derived. 相似文献
8.
A three-component fluid model of the Universe during the recombination era is analysed for =
c
(
c
is the critical density). In addition to the well-known instability of the Jeans mode at 109
M
, we find two more unstable modes at 1012
M
. 相似文献
9.
The 5-dimensional Jordan-Brans-Dicke cosmologies in vacuum are found for the Bianchi type I metric, their relation with general relativity cosmologies is studied. Two solutions are possible, both produce effective pressure and energy density in the 4-dimensional G.R.-universes. One is a power-law relation, with two cases, the first one is forp
eff=eff and the other forp
eff=eff(– 1 < < 1) has a behaviour as the open flat universe. The second solution is an exponential only valid forp
eff=–eff. In all cases the three-space expansion reaches infinity ast and the fifth dimension can be made to decrease approaching zero. The scalar field can increase or decrease with time. 相似文献
10.
Analytic structure of high-density steady isothermal spheres is discussed using the TOV equation of hydrostatic equilibrium which satisfies an equation of state of the kind:P = K
g
, =
g
c
2.Approximate analytical solutions to the Tolman-Oppenheimer-Volkoff (TOV) equations of hydrostatic equilibrium in (, ), (,U) and (u, v) phase planes in concise and simple form useful for short computer programmes or on small calculator, have been given. In Figures 1, 2, and 3, respectively, we display the qualitative behaviours of the ratio of gas density
g
to the central density
gc
,
g
/
gc
; pressureP to the
gc
,P/
gc
; and the metric componente
–, for three representative general relativistic (GR) isothermal configurations =0.1, 0.2, and 0.3. Figure 4 shows the solution curve (, ) for =0.1, 0.2, and 0.3 (=0 represents the classical (Newtonian) curve). Numerical values of physical quantitiesv (=4r
2
P
*(r)), in steps ofu (=M(r)/r)=0.03, and the mass functionU, in steps of =0.2 (dimensionless radial distance), are given, respectively, in Tables I and II. Other interesting features of the configurations, such as ratio of gravitational radius 2GM/c
2 to the coordinate radiusR, mass distributionM(r)/M, pressure (or density) distributionP/P
c
, binding energy (B.E.), etc., have also been incorporated in the text. It has further been shown that velocity of sound inside the configurations is always less than the velocity of light.Part of the work done at Azerbaijan State University, Baku, U.S.S.R., and Mosul University, Mosul, Iraq, 1985-1986 相似文献
11.
In a two-fluid component universe consisting of visible matter and neutrinos, the developed features of perturbations in the two components are quite different. If the densities 1 and 2, and the Jeans lengths 1J and 2J of the two components satisfy the relations 12, 1J2J, the developed inhomogeneities in the non-dominant component 1 are larger than those in the dominant component 2. Moreover, the increase of perturbations is in some situations not monotonous but oscillatory, and such oscillations in the two components are contrary. 相似文献
12.
The CCW method (see Chester, 1854; Chisnell, 1955; Whitham, 1958) has been used to investigate the propagation of diverging shock waves through an ideal gas under its own gravitation having an initial density distribution
0 = exp(–r , where is the density at the plane/axis/origin, respectively, for plane, cylindrical, and spherical symmetry of the shock and, is non-dimensional constant, for the two situations: viz., (i) when the shock is weak and (ii) when it is strong, simultaneously. Analytical relations for shock velocity and shock strength have been obtained. Expressions for the pressure, the density and the particle velocity immediately behind the shock have been derived. Their numberical estimates for plane and cylindrical symmetry of the shock, have been computed. 相似文献
13.
Relativistic stellar structures can be obtained both analytically and by computation, but all these models do not stand the tests of physical reality. It is shown that for a physically reasonable solution d/dr -r and d(e
v
/dr r near the centre, d(P/)/dr<-0 and (dP/d)>-(P/). If we change the variabler tox=Cr
2, whereC is a constant, the field equations are reduced to a form which is easier to solve. A new set of exact solutions is obtained by consideringe
v
(1-x)
n
. Also, a method has been given to obtain generalized solution.It is shown that the solution discussed by Durgapal and Rawat (1980) is the only exact solution which in its most generalized form for a given density distribution stands all the tests of physical reality and for which both (P/) and (dP/d) decrase with increasing value ofr.Neutron star model is proposed by assuming >-2×1014g cm–3. Two specific cases are considered, viz.,P<-1/3 and dP/d<-1, respectively. The structures are found to be bound and stable under radial perturbations. The models have been studied for slow rotation and the mass of the Crab pulsar has been estimated for different mechanisms. 相似文献
14.
The process of re-escalation of the scalar field as R
3, the energy density as R
3, and the pressurep aspR
3P, lends itself to obtain a reduced equation that represents, for a wide variety of equations of state, the cosmological evolution of an homogeneous and isotropic, flat Universe. A particular solution to this equation is presented. 相似文献
15.
Strange quark stars with a crust and strange dwarfs consisting of a compact strange quark core and an extended crust are investigated in terms of a bag model. The crust, which consists of atomic nuclei and degenerate electrons, has a limiting density of cr=drip=4.3·1011 g/cm3. A series of configurations are calculated for two sets of bag model parameters and three different values of cr (109 g/cm3 cr drip) to find the dependence of a star's mass M and radius R on the central density. Sequences of stars ranging from compact strange stars to extended strange dwarfs are constructed out of strange quark matter with a crust. The effect of the bag model parameters and limiting crust density cr on the parameters of the strange stars and strange dwarfs is examined. The strange dwarfs are compared with ordinary white dwarfs and observational differences between the two are pointed out. 相似文献
16.
Conclusions In the Newtonian case we have obtained an isotropic self-consistent distribution of gravitationally interacting point masses which satisfies the transport equation without collisions, and the gravitational equation for an arbitrary powerfunction density distribution =r–s, s<3.For =r–2 the analogous self-consistent solution was obtained for the anisotropic distribution function both in Newtonian and GTR cases.The GTR solutions with =r–2 have central redshifts which increase without limit in accordance with the law 1+zr–1/ as we approach the center. In the isotropic case, they appear to be stable when the mean velocities are much less than the velocity of light u<0.2c, >21.The hydrodynamic GTR solution was found for a perfect gas at constant temperature (but variable T=T(g00)1/2) which also has z for r0.We should like to thank K. Thorne, L. Hazin, and M. Podurets for valuable discussions. K. Thorne was particularly helpful in supplying unpublished results on circular orbits obtained by American authors.Astrofizika, Vol. 5, No. 2, pp. 223–234, 1969 相似文献
17.
Effect of overtaking disturbances on the propagation of a spherical shock wave in self gravitating gas has been studied by the technique developed by the first author [Mod. Meas. Cont. B,46(4), 1 (1992)]. The analytical expressions for modified shock velocity and shock strength have been obtained for an initial density distribution0 =r
–w, where is the density at the axis of symmetry andw is a constant; simultaneously, for the two cases viz.; (i) when the shock is strong and ii) when it is weak. The results accomplished here have been compared with those for freely propagation of shock.It is observed that the conclusions arrived at here agree with experimental observations. Finally, the modified expressions for the pressure, the density and the particle velocity immediately behind the shock have also been derived from, for both cases. 相似文献
18.
We study the classical problem of two-dimensional motion of a particle in the field of a central force proportional to a real power of the distancer. for negative energy and (0, 2), each energy levelI
h is foliated by the invariant toriI
hc of constant angular momentumc and, by Liouville-Arnold's theorem, the flow on eachI
hc is conjugated to a linear flow of rotation number
h
(c).A well-known result asserts that if we require
h
(c) to be rational for every value ofh andc, the, must be equal to one (Kepler's problem). In this paper we prove that for almost every (0, 2)
h
(c) is a non-constant continuous function ofc, for everyh<0. In particular, we deduce that motion under central potentials is generically non-periodic.Partially supported by CIRIT under grant No. EE88/2. 相似文献
19.
We determine the radial component of the supergranular flow velocity by examining the center-to-limb variation of the Doppler velocity signal. We acquire individual Doppler images obtained with the MDI instrument on the SOHO spacecraft and process them to remove the p-mode oscillation signal, the axisymmetric flows, the convective blueshift signal, and instrumental artifacts. The remaining Doppler signal contains only non-axisymmetric flow structures. The Doppler signal from the horizontal flows in these structures varies like sin, where is the heliocentric angle from disk center. The Doppler signal from radial flows varies like cos. We fit the center-to-limb variation of the mean squared velocity signal to a straight line in sin2 over the central portion of the disk. The intercept of this line at disk center gives the amplitude of the radial component of the flow. The slope of the line gives the amplitude of the horizontal component. We find that the radial flows for typical supergranules have speeds about 10% that of their associated horizontal flows or about 30 m s–1. The ratio of the radial to horizontal flow speed increases from 9% to about 18% as the size of the structure decreases from >60 Mm to 5 Mm. We use data simulations to check these results and find a ratio that increases from 5% to only about 12% over the same range of sizes. These smaller ratios are attributed to an underestimation of the horizontal flow speeds due to the fact that the transverse component of the horizontal flow is not detected by Doppler measurements. 相似文献
20.
C.P. Singh 《Astrophysics and Space Science》2001,275(4):377-383
A spatially homogeneous and isotropic Robertson-Walker model withzero-curvature of the universe is studied within the frame-work of Lyra'smanifold. The gauge-function in Lyra's manifold is taken to betime-dependent. Exact solutions of Einstein equations are obtained for twodifferent early phases of the universe viz. Inflationary phase andradiation-dominated phase by using `gamma-law' equation of statep = ( - 1) . The -index, describing the material content,varies continuously with cosmic time so that in the course of itsevolution, the universe goes through a transition from an inflationaryphase to a radiation-dominated phase. The physical properties of themodels are also discussed. 相似文献