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1.
The paper deals with massive fluid spheres with an isothermal core (having finite central density) and a polytropic envelope in terms of the General Relativity. The matching of the solutions in the core and envelope has been done using Bondi's condition,H=0 and also without it. The study reveals that since this condition does not correspond to any particular physical situation the maximum values of fractional core size, fractional core mass and the redshift do not occur atH=0, but that they occur at some other point. Within the permissible physical conditions (dP/dρ≤1) the maximum values ofM core/M,R core/R and the surface redshift, for an isothermal coreP=ρ/3, are respectively 0.473, 0.554, and 0.565. Using the conditionH=0, it has been shown that for isothermal cores corresponding to the equation of the stateP≥0.6ρ, the configurations are pulsationally unstable.  相似文献   

2.
We present a well behaved class of Charge Analogue of Heintzmann (Z. Phys. 228:489, 1969) solution. This solution describes charge fluid balls with positively finite central pressure and positively finite central density ; their ratio is less than one and causality condition is obeyed at the centre. The outmarch of pressure, density, pressure-density ratio and the adiabatic speed of sound is monotonically decreasing, however, the electric intensity is monotonically increasing in nature. The solution gives us wide range of constant K (1.25≤K≤15) for which the solution is well behaved and therefore, suitable for modeling of super dense star. For this solution the mass of a star is maximized with all degrees of suitability and by assuming the surface density ρ b =2×1014 g/cm3. Corresponding to K=1.25 and X=0.42, the maximum mass of the star comes out to be 3.64M Θ with linear dimension 24.31 km and central redshift 1.5316.  相似文献   

3.
Using Shell-Model Monte Carlo (SMMC) method and Random Phase Approximation (RPA) theory, the electron capture (EC) and the electron capture cross section (ECCS) of nuclei 55Co and 56Ni are investigated. We also discuss the rates of the change of electron fraction (RCEF) and the error factor C, which is compared our results with those of AFUD, which calculated by the method of Aufderheide. The results show that the ECCS and the EC rates for 55Co and 56Ni increased about four orders of magnitude at relative high temperature (such as T 9=5,7,9). On the other hand, the RCEF for two nuclides decreased greatly, and even exceed four orders of magnitude. The error factor shows ours is agreed reasonably well with AUFD under the higher density surroundings (e.g. ρ7=106, Y e =0.43; ρ7=506, Y e =0.42; ρ7=4010, Y e =0.41). But under the lower density surroundings (e.g. ρ7=3.36, Y e =0.48) the maximum error is ～14.5 % for 55Co but is ～14.0 % for 56Ni. The error is ～9.5 % and ～9.0 % for 55Co, 56Ni at ρ7=5.86, Y e =0.47 respectively.  相似文献   

4.
To reconstruct dark energy models the redshift z eq , marking the end of radiation era and the beginning of matter-dominated era, can play a role as important as z t , the redshift at which deceleration parameter experiences a signature flip. To implement the idea we propose a variable equation of state for matter that can bring a smooth transition from radiation to matter-dominated era in a single model. A popular Λ∝ ρ dark energy model is chosen for demonstration but found to be unacceptable. An alternative Λ∝ ρ a 3 model is proposed and found to be more close to observation.  相似文献   

5.
The apparatus of correlation gamma function (Γ*(r)) is used to analyze volume-limited samples from the DR4 Main Galaxy Sample of the SDSS survey with the aim of determining the characteristic scales of galaxy clustering. Up to 20h ?1 Mpc (H 0 = 65 km s?1 Mpc?1), the distribution of galaxies is described by a power-law density—distance dependence, Γ*(r) ∝ r ?γ , with an index γ ≈ 1.0. A change in the state of clustering (a significant deviation from the power law) was found on a scale of (20–25) h ?1 Mpc. The distribution of SDSS galaxies becomes homogeneous (γ ～ 0) from a scale of ～60h ?1 Mpc. The dependence of γ on the luminosity of galaxies in volume-limited samples was obtained. The power-law index γ increases with decreasing absolute magnitude of sample galaxies M abs. At M abs ～ ?21.4, which corresponds to the characteristic value M r * of the SDSS luminosity function, this dependence exhibits a break followed by a more rapid increase in γ.  相似文献   

6.
The paper presents a variety of classes of interior solutions of Einstein–Maxwell field equations of general relativity for a static, spherically symmetric distribution of the charged fluid with well behaved nature. These classes of solutions describe perfect fluid balls with positively finite central pressure, positively finite central density; their ratio is less than one and causality condition is obeyed at the center. The outmarch of pressure, density, pressure–density ratio and the adiabatic speed of sound is monotonically decreasing for these solutions. Keeping in view of well behaved nature of these solutions, two new classes of solutions are being studied extensively. Moreover, these classes of solutions give us wide range of constant K for which the solutions are well behaved hence, suitable for modeling of super dense star. For solution (I1) the mass of a star is maximized with all degree of suitability and by assuming the surface density ρ b =2×1014 g/cm3 corresponding to K=1.19 and X=0.20, the maximum mass of the star comes out to be 2.5M Θ with linear dimension 25.29 Km and central redshift 0.2802. It has been observed that with the increase of charge parameter K, the mass of the star also increases. For n=4,5,6,7, the charged solutions are well behaved with their neutral counterparts however, for n=1,2,3, the charged solution are well behaved but their neutral counterparts are not well behaved.  相似文献   

7.
We present three new categories of exact and spherically symmetric Solutions with finite central parameters of the general relativistic field equations. Two well behaved solutions in curvature coordinates first category are being studied extensively. These solutions describe perfect fluid balls with positively finite central pressure, positively finite central density; their ratio is less than one and causality condition is obeyed at the centre. The outmarch of pressure, density, pressure-density ratio and the adiabatic speed of sound is monotonically decreasing for these solutions. Keeping in view of well behaved nature of these solutions, one of the solution (I1) is studied extensively. The solution (I1) gives us wide range of Schwarzschild parameter u (0.138≤u≤0.263), for which the solution is well behaved hence, suitable for modeling of Neutron star. For this solution the mass of Neutron star is maximized with all degree of suitability and by assuming the surface density ρ b =2×1014 g/cm3. Corresponding to u=0.263, the maximum mass of Neutron star comes out to be 3.369 M Θ with linear dimension 37.77 km and central and surface redshifts are 4.858 and 0.4524 respectively. We also study some well known regular solutions (T-4, D-1, D-2, H, A, P) of Einstein’s field equations in curvature coordinates with the feature of constant adiabatic sound speed. We have chosen those values of Schwarzschild parameter u for which, these solutions describe perfect fluid balls realistic equations of state. However, except (P) solution, all these solutions have monotonically non-decreasing feature of adiabatic sound speed. Hence (P) solution is having a well behaved model for uniform radial motion of sound. Keeping in view of well behaved nature of the solution for this feature and assuming the surface density; ρ b =2×1014 g/cm3, the maximum mass of Neutron star comes out to be 1.34 M Θ with linear dimension 28.74 km. Corresponding central and surface redshifts are 1.002 and 0.1752 respectively.  相似文献   

8.
Measurements of the bulk density, grain density, porosity, and magnetic susceptibility of 19 Gao-Guenie H5 chondrite meteorite samples are presented. We find average values of bulk density 〈ρbulk〉=3.46±0.07 g/cm3, grain density 〈ρgrain〉=3.53±0.08 g/cm3, porosity 〈P(%)〉=2.46±1.39, and bulk mass magnetic susceptibility 〈log χ〉=5.23±0.11. Measurements of the specific heat capacity for a 3.01-g Gao-Guenie sample, a 61.37-g Gao-Guenie sample, a 62.35-g Jilin H5 chondrite meteorite sample, and a 51.37-g Sikhote-Alin IIAB Iron meteorite sample are also presented. Temperature interpolation formula are further provided for the specific heat capacity, thermal conductivity, and thermal diffusivity of the 3.01-g Gao-Guenie sample in the temperature range 300<T (K)<800. We briefly review the possible effects of the newly deduced specific heat and thermal conductivity values on the ablation of meteoroids within the Earth's atmosphere, the modeling of asteroid interiors and the orbital evolution of meteoroids through the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect.  相似文献   

9.
A family of well behaved perfect fluid balls has been derived starting with the metric potential g 44=B(1+Cr 2) n for all positive integral values of n. For n≥4, the members of this family are seen to satisfy the various physical conditions e.g. c 2 ρ≥p≥0,dp/dr<0,dρ/dr<0, along with the velocity of sound \((\sqrt{dp/c^{2}d\rho} )< 1\) and the adiabatic index ((p+c 2 ρ)/p)(dp/(c 2 dρ))>1. Also the pressure, energy density, velocity of sound and ratio of pressure and energy density are of monotonically decreasing towards the pressure free interface (r=a). The fluid balls join smoothly with the Schwarzschild exterior model at r=a. The well behaved perfect fluid balls so obtained are utilised to construct the superdense star models with their surface density 2×1014  gm/cm3. We have found that the maximum mass of the fluid balls corresponding to various values of n are decreasing with the increasing values of n. Over all maximum mass for the whole family turns out to be 4.1848M Θ and the corresponding radius as 19.4144 km while the red shift at the centre and red shift at surface as Z 0=1.6459 and Z a =0.6538 respectively this all happens for n=4. It is interesting to note that for higher values of n viz n≥170, the physical data start merging with that of Kuchowicz superdense star models and hence the family of fluid models tends to the Kuchowicz fluid models as n→∞. Consequently the maximum mass of the family of solution can not be less than 1.6096 M Θ which is the maximum mass occupied by the Kuchowicz superdense ball. Hence each member of the family for n≥4 provides the astrophysical objects like White dwarfs, Quark star, typical neutron star.  相似文献   

10.
The paper presents a class of interior solutions of Einstein–Maxwell field equations of general relativity for a static, spherically symmetric distribution of the charged fluid. This class of solutions describes well behaved charged fluid balls. The class of solutions gives us wide range of parameter K (0≤K≤42) for which the solution is well behaved hence, suitable for modeling of super dense star. For this solution the mass of a star is maximized with all degree of suitability and by assuming the surface density ρ b =2×1014 g/cm3. Corresponding to K=2 and X=0.30, the maximum mass of the star comes out to be 4.96 M Θ with linear dimension 34.16 km and central redshift and surface redshift 2.1033 and 0.683 respectively. In absence of the charge we are left behind with the well behaved fourth model of Durgapal (J. Phys., A, Math. Gen. 15:2637, 1982).  相似文献   

11.
A statistical study of 77 solar active regions (ARs) is conducted to investigate the existence of identifiable correlations between the subsurface structural disturbances and the activity level of the active regions. The disturbances examined in this study are 〈|δΓ 1/Γ 1|〉, 〈|δc 2/c 2|〉, and 〈|δc 2/c 2?δΓ 1/Γ 1|〉, where Γ 1 and c are the thermodynamic properties of first adiabatic index and sound speed modified by magnetic field, respectively. The averages are over three depth layers: 0.975–0.98R ⊙, 0.98–0.99R ⊙ and 0.99–0.995R ⊙ to represent the structural disturbances in that layer. The level of the surface magnetic activity is measured by the Magnetic Activity Index (MAI) of active region and the relative and absolute MAI differences (rdMAI and dMAI) between the active and quiet regions. The eruptivity of each active region is quantified by its Flare Index, total number of coronal mass ejections (CMEs), and total kinetic energy of the CMEs. The existence and level of the correlations are evaluated by scatter plots and correlation coefficients. No definitive correlation can be claimed from the results. While a weak positive trend is visible between dMAI and 〈|δΓ 1/Γ 1|〉 and 〈|δc 2/c 2|〉 in the layer 0.975–0.98R ⊙, their correlation levels, being approximately 0.6, are not sufficiently high to justify the correlation. Some subsurface disturbances are seen to increase with eruptivity indices among ARs with high eruptivity. The statistical significance of such trend, however, cannot be ascertained due to the small number of very eruptive ARs in our sample.  相似文献   

12.
Pressure dependences of the volume scattering coefficient of aerosol in the atmosphere of Jupiter σ a (P) are presented. In calculations carried out with separating the gaseous and aerosol absorption, the absorption of light in the continuous spectrum was taken into account. In the analysis, the spectrophotometric data of Jupiter for the absorption bands of methane at 727 and 619 nm—the geometric albedo (measured in 1993) and the reflectivity of some latitudinal details (measured in 2013)—were used. At high tropospheric levels, in the pressure range from 0.4 to 2 bar, the dependences σ a (P) for the integral disk and latitude belts of the giant planet turned out to be similar. In this part of the atmosphere, the three thickest cloud layers were found; in these layers, within the pressure range from 0.8 to 1.33 bar in the North and South Temperature Belts (NTB and STB), respectively, the values of the coefficient σ a (P) are maximum. In the pressure interval from 2 to 4 bar, in the analyzed latitude belts except the NTB and STB, the forth aerosol layer was found; its altitude position and vertical structure substantially differ from belt to belt. One more aerosol layer probably exists deeper in the atmosphere; its initial level and extension differ in different latitude belts. Most of the investigated latitude belts exhibit the spectral dependence of σ a (P) at the atmospheric levels, where the pressure exceeds 3 bar. This probably points to the change in size or nature of aerosol particles.  相似文献   

13.
We carried out the investigation of the properties of features seen within superluminal sources often referred to as components. Our result indicates a fairly strong correlation of r～0.76 between component radial distance L and component size ?. Assumption of simple ballistic motion and free adiabatic expansion, enabled us to use the observed jet component parameters to constrain the Doppler factor, Lorentz factor and the lower limit to the viewing angle with respect to a distant observer. The estimated average Doppler factor, Lorentz factor and viewing angle respectively are 10.3±5.0, 18.3±6.2 and 3.7±2.3 for Γ=4/3; while the values obtained for Γ=5/3 are 12.2±5.9,17.2±5.1 and 2.9±1.6, where Γ is the adiabatic index. The large scatter in our results may be due to the uncertainties introduced by the assumptions made.  相似文献   

14.
The paper presents a new class of parametric interior solutions of Einstein–Maxwell field equations in general relativity for a static spherically symmetric distribution of a charged perfect fluid with a particular form of electric field intensity. This solution gives us wide range of parameter, K (0.69≤K≤7.1), for which the solution is well behaved hence, suitable for modeling of superdense star. For this solution the gravitational mass of a superdense object is maximized with all degree of suitability by assuming the surface density of the star equal to the normal nuclear density ρ nm=2.5×1017kg?m?3. By this model we obtain the mass of the Crab pulsar M Crab=1.401M ⊙ and the radius, R Crab=12.98 km constraining the moment of inertia I NS,38>1.61 for the conservative estimate of Crab nebula mass 2M ⊙ and M Crab=2.0156M ⊙ with radius, R Crab=14.07 km constraining the moment of inertia I NS,38>3.04 for the newest estimate of Crab nebula mass 4.6M ⊙ which are quite well in agreement with the possible values of mass and radius of Crab pulsar. Besides this, our model yields the moments of inertia for PSR J0737-3039A and PSR J0737-3039B are I A,38=1.4624 and I B,38=1.2689 respectively. It has been observed that under well behaved conditions this class of parametric solution gives us the maximum gravitational mass of causal superdense object 2.8020M ⊙ with radius 14.49 km, surface redshift z R =0.4319, charge Q=4.67×1020 C, and central density ρ c =2.68ρ nm.  相似文献   

15.
Having analyzed the spectrum of the quasar PKS 1232+0.82 taken by Petitjean et al. (2000), we identified HD molecular lines in an absorption system at redshift z=2.3377. We estimated the column density of HD molecules in this system, N(HD) = (1?4) × 1014cm?2. The excitation temperature of the first rotational level J=1 relative to the ground state J=0 is T ex=70 ± 7 K. As far as we know, this is the first detection of HD molecules at high redshift.  相似文献   

16.
A Fourier analysis on galaxy number counts from redshift data of both the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey indicates that galaxies have preferred periodic redshift spacings of Δz= 0.0102, 0.0246, and 0.0448 in the SDSS and strong agreement with the results from the 2dF GRS. The redshift spacings are confirmed by the mass density fluctuations, the power spectrum P(z) and N pairs calculations. Application of the Hubble law results in galaxies preferentially located on co-moving concentric shells with periodic spacings. The combined results from both surveys indicate regular co-moving radial distance spacings of 31.7±1.8 h?1?Mpc, 73.4±5.8 h?1?Mpc and 127±21 h?1? Mpc. The results are consistent with oscillations in the expansion rate of the universe over past epochs.  相似文献   

17.
We employ ring-diagram analysis to study the sub-surface thermal structure of active regions. We present results using a large number of active regions over the course of Solar Cycle 23. We present both traditional inversions of ring-diagram frequency differences, with a total sample size of 264, and a statistical study using Principal Component Analysis. We confirm earlier results on smaller samples that sound speed and adiabatic index are changed below regions of strong magnetic field. We find that sound speed is decreased in the region between approximately r=0.99?R ⊙ and r=0.995?R ⊙ (depths of 3 Mm to 7 Mm) and increased in the region between r=0.97?R ⊙ and r=0.985?R ⊙ (depths of 11 Mm to 21 Mm). The adiabatic index [Γ1] is enhanced in the same deeper layers where sound-speed enhancement is seen. A weak decrease in adiabatic index is seen in the shallower layers in many active regions. We find that the magnitudes of these perturbations depend on the strength of the surface magnetic field, but we find a great deal of scatter in this relation, implying that other factors may be relevant.  相似文献   

18.
Monthly coronal mass ejection (CME) counts, – for all CMEs and CMEs with widths >?30°, – and monthly averaged speeds for the events in these two groups were compared with both the monthly averaged cosmic ray intensity and the monthly sunspot number. The monthly P i-index, which is a linear combination of monthly CME count rate and average speed, was also compared with the cosmic ray intensity and sunspot number. The main finding is that narrow CMEs, which were numerous during 2007?–?2009, are ineffective for modulation. A cross-correlation analysis, calculating both the Pearson (r) product–moment correlation coefficient and the Spearman (ρ) rank correlation coefficient, has been used. Between all CMEs and cosmic ray intensity we found correlation coefficients r=??0.49 and ρ=??0.46, while between CMEs with widths >?30° and cosmic ray intensity we found r=??0.75 and ρ=??0.77, which implies a significant increase. Finally, the best expression for the P i-index for the examined period was analyzed. The highly anticorrelated behavior among this CME index, the cosmic ray intensity (r=??0.84 and ρ=??0.83), and the sunspot number (r=+?0.82 and ρ=+?0.89) suggests that the first one is a very useful solar–heliospheric parameter for heliospheric and space weather models in general.  相似文献   

19.
A strong emission line at 6703 Å has been detected in the optical spectrum for the host galaxy (R = 23.1) of the radio source RC J0311+0507 (4C+04.11). This radio galaxy, with a spectral index of 1.31 in the frequency range 365–4850 MHz, is one of the ultrasteep-spectrum objects from the deep survey of a sky strip conducted with RATAN-600 in 1980–1981. We present arguments in favor of the identification of this line with Lyα at redshift z = 4.514. In this case, the object belongs to the group of extremely distant radio galaxies of ultrahigh radio luminosity (P 1400 = 1.3 × 1029 W Hz?1). Such power can be provided only by a fairly massive black hole (～109 M⊙) that formed in a time less than the age of the Universe at the observed z (1.3 Gyr) or had a primordial origin.  相似文献   

20.
In this paper first ever we have developed a class of well behaved charged fluid spheres expressed by a space time with its hypersurfaces $t = \operatorname {const}$ . as spheroid for the case 0<K<1 with surface density 2×1014 gm/cm3. The same utilized to construct a superdense star and seen that star satisfies all well behaved condition for 0<K≤0.038. The maximum mass occupied and the corresponding radius are found to be 4.830982M Θ and 20.7612 km respectively. The redshift at the center and on the surface is given z 0=0.425367 and z a =0.240901.  相似文献   

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