首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 906 毫秒
1.
Rahaman et al. (Astrophys. Space. Sci. 331:191–197, 2010) discussed some classical electron models (CEM) in general relativity. Bijalwan (Astrophys. Space. Sci. 334:139–143, 2011) present a general exact solution of the Einstein-Maxwell equations in terms of pressure. We showed that charged fluid solutions in terms of pressure are not reducible to a well behaved neutral counter part for a spatial component of metrice λ . Hence, these solutions represent an electron model in general relativity. We illustrated solutions in terms of pressure briefly with de-Sitter equation of state and charged analogues of Kohler Chao interior solution as a special cases.  相似文献   

2.
Recently, Bijalwan (Astrophys. Space Sci. doi:, 2011) discussed all important solutions of charged fluid spheres with pressure and Gupta et al. (Astrophys. Space Sci. doi:, 2010) found first closed form solutions of charged Vaidya-Tikekar (V-T) type super-dense star. We extend here the approach evolved by Bijalwan (Astrophys. Space Sci. doi:, 2011) to find all possible closed form solutions of V-T type super-dense stars. The existing solutions of Vaidya-Tikekar type charged fluid spheres considering particular form of electric field intensity are being used to model massive stars. Infact at present maximum masses of the star models are found to be 8.223931M Θ and 8.460857M Θ subject to ultra-relativistic and non-relativistic conditions respectively. But these stars with such are large masses are not well behaved due to decreasing velocity of sound in the interior of star. We present new results concerning the existence of static, electrically charged perfect fluid spheres that have a regular interior. It is observed that electric intensity used in this article can be used to model superdense stars with ultrahigh surface density of the order 2×1014 gm/cm3 which may have maximum mass 7.26368240M Θ for ultra-relativistic condition and velocity of sound found to be decreasing towards pressure free interface. We solve the Einstein-Maxwell equations considering a general barotropic equation of state with pressure. For brevity we don’t present a detailed analysis of the derived solutions in this paper.  相似文献   

3.
Recently, Bijalwan (Astrophys. Space Sci., doi:, 2011a) discussed charged fluid spheres with pressure while Bijalwan and Gupta (Astrophys. Space Sci. 317, 251–260, 2008) suggested using a monotonically decreasing function f to generate all possible physically viable charged analogues of Schwarzschild interior solutions analytically. They discussed some previously known and new solutions for Schwarzschild parameter u( = \fracGMc2a ) ￡ 0.142u( =\frac{GM}{c^{2}a} ) \le 0.142, a being radius of star. In this paper we investigate wide range of u by generating a class of solutions that are well behaved and suitable for modeling Neutron star charge matter. We have exploited the range u≤0.142 by considering pressure p=p(ω) and f = ( f0(1 - \fracR2(1 - w)a2) +fa\fracR2(1 - w)a2 )f = ( f_{0}(1 - \frac{R^{2}(1 - \omega )}{a^{2}}) +f_{a}\frac{R^{2}(1 - \omega )}{a^{2}} ), where w = 1 -\fracr2R2\omega = 1 -\frac{r^{2}}{R^{2}} to explore new class of solutions. Hence, class of charged analogues of Schwarzschild interior is found for barotropic equation of state relating the radial pressure to the energy density. The analytical models thus found are well behaved with surface red shift z s ≤0.181, central red shift z c ≤0.282, mass to radius ratio M/a≤0.149, total charge to total mass ratio e/M≤0.807 and satisfy Andreasson’s (Commun. Math. Phys. 288, 715–730, 2009) stability condition. Red-shift, velocity of sound and p/c 2 ρ are monotonically decreasing towards the surface while adiabatic index is monotonically increasing. The maximum mass found to be 1.512 M Θ with linear dimension 14.964 km. Class of charged analogues of Schwarzschild interior discussed in this paper doesn’t have neutral counter part. These solutions completely describe interior of a stable Neutron star charge matter since at centre the charge distribution is zero, e/M≤0.807 and a typical neutral Neutron star has mass between 1.35 and about 2.1 solar mass, with a corresponding radius of about 12 km (Kiziltan et al., [astro-ph.GA], 2010).  相似文献   

4.
Recently Varvoglis and Hadjidemetriou (Astrophys. Space Sci. doi:, 2012; hereafter referred to as paper VH) have raised two points concerning the model of the restricted three-body problem with variable mass presented in our paper (Zhang et al. in Astrophys. Space Sci. 337:107, 2012; hereafter referred to as paper ZZX) and made intensive investigations of this model. These points and investigations are very useful and here we provide some explanation and supplementary specification regarding the model presented in the paper ZZX.  相似文献   

5.
We obtain a new parametric class of exact solutions of Einstein–Maxwell field equations which are well behaved. We present a charged super-dense star model after prescribing particular forms of the metric potential and electric intensity. The metric describing the super dense stars joins smoothly with the Reissner–Nordstrom metric at the pressure free boundary. The electric density assumed is where n may take the values 0,1,2,3,4 and so on and K is a positive constant. For n=0,1 we rediscover the solutions by Gupta and Maurya (Astrophys. Space Sci. 334(1):155, 2011) and Fuloria et al. (J. Math. 2:1156, 2011) respectively. The solution for n=2 have been discussed extensively keeping in view of well behaved nature of the charged solution of Einstein–Maxwell field equations. The solution for n=3 and n=4 can be also studied likewise. In absence of the charge we are left behind with the regular and well behaved fifth model of Durgapal (J. Phys. A 15:2637, 1982). The outmarch of pressure, density, pressure-density ratio and the velocity of sound is monotonically decreasing, however, the electric intensity is monotonically increasing in nature. For this class of solutions the mass of a star is maximized with all degree of suitability, compatible with Neutron stars and Pulsars.  相似文献   

6.
After reviewing the scalar-tensor lambda-accelerating power-law solutions by Berman (Astrophys. Space Sci. 323:103, 2009a), we obtain solutions for the amplification of gravitational waves in the models. The solutions consider a perfect gas equation of state, with cosmic pressure proportional to the energy density, the proportionality constant being smaller than −2/3.  相似文献   

7.
Motivated by earlier studies (Tiwari et al. in Astrophys. Space Sci. 182:105, 1984; Herrera and Varela in Phys. Lett. 189:11, 1994), we model electron as a spherically symmetric charged perfect fluid distribution of matter. The existing model is extended assuming a matter source that is characterized by quadratic equation of state in the context of general theory of relativity. For the suitable choices of the parameters, our charged fluid models almost satisfy the physical properties of electron.  相似文献   

8.
We point out here that all the solutions presented in Rahaman et al. (Astrophys. Space Sci. 331:191–197, 2011) are incorrect and do not satisfy the system of governing Einstein-Maxwell field equations.  相似文献   

9.
In a previous paper (Berman, in Astrophys. Space Sci., 2011), we showed how to prove the two Pioneers Anomalies, and now we add the fly-bys, by means of a rotating Universe. We discuss Einstein’s Machian program, which we find as being fullfilled. Godlowski et al. (Los Alamos Archives, 2003) idea for a rotating General Relativistic Universe, led us to the adopted model. Updated evidence on rotation is cited (Godlowski, in Los Alamos Archives, 2011; Ni in Phys. Rev. Lett. 107(5):051103, 2011). We conclude that a rotating and expanding Universe may be the unique solution to the apparent divergences between Einstein and Mach. This is cosmologically important.  相似文献   

10.
Very recently (Banerjee et al. in Astrophys. Space, doi:, 2011) the statistics of geomagnetic Disturbance storm (Dst) index have been addressed, and the conclusion from this analysis suggests that the underlying dynamical process can be modeled as a fractional Brownian motion with persistent long-range correlations. In this comment we expose several misconceptions and flaws in the statistical analysis of that work. On the basis of these arguments, the former conclusion should be revisited.  相似文献   

11.
The Local Group galaxies enable us to study the impact of metallicity on the structure and evolution of massive stars through spectroscopic analyses. However, color-based target selection for spectroscopy (in absence of known spectral types), though relatively successful, usually produces lists dominated by B-type modest-mass stars. We have developed a friends of friends code to find OB associations in Local Group galaxies (Garcia et al. in Astron. Astrophys. 502:1015, 2009; Bull. Soc. R. Sci. Liege 80:381, 2011a). The interpretation of the association’s color-magnitude diagrams (CMDs) and the automatic determination of evolutionary masses for the members, allow a more insightful choice of candidates for spectroscopy and to spot out potential advanced evolutionary stages (Garcia et al. in Astron. Astrophys. 523:A23, 2010). We show our results on the dwarf irregular IC 1613 as illustration of the potential of the method.  相似文献   

12.
In the framework of ‘microscopic’ theory of black holes (J. Phys. Soc. Jpn. Suppl. B 70, 84, 2001; Astrophys. USSR 4, 659, 1996; 35, 335, 1991, 33, 143, 1990, 31, 345, 1989a; Astrophys. Space Sci. 1, 1992; Dokl. Akad. Nauk USSR 309, 97, 1989b), and references therein, we address the ‘pre-radiation time’ (PRT) of neutrinos from black holes, which implies the lapse of time from black hole’s birth till radiation of an extremely high energy neutrinos. For post-PRT lifetime, the black hole no longer holds as a region of spacetime that cannot communicate with the external universe. We study main features of spherical accretion onto central BH and infer a mass accretion rate onto it, and, further, calculate the resulting PRT versus bolometric luminosity due to accretion onto black hole. We estimate the PRTs of AGN black holes, with the well-determined masses and bolometric luminosities, collected from the literature by Woo Jong-Hak and Urry (Astrophys. J. 579, 530, 2002) on which this paper is partially based. The simulations for the black holes of masses M BH ≃(1.1⋅106 ÷4.2⋅109) M ⊙ give the values of PRTs varying in the range of about T BH ≃(4.3⋅105 ÷5.6⋅1011) yr. The derived PRTs for the 60 AGN black holes are longer than the age of the universe (∼13.7 Gyr) favored today. At present, some of remaining 174 BHs may radiate neutrinos. However, these results would be underestimated if the reservoir of gas for accretion in the galaxy center is quite modest, and no obvious way to feed the BHs with substantial accretion.  相似文献   

13.
Recent numerical investigations of wave propagation near coronal magnetic null points (McLaughlin and Hood: Astron. Astrophys. 459, 641, 2006) have indicated how a fast MHD wave partially converts into a slow MHD wave as the disturbance passes from a low-β plasma to a high-β plasma. This is a complex process and a clear understanding of the conversion mechanism requires the detailed investigation of a simpler model. An investigation of mode conversion in a stratified, isothermal atmosphere with a uniform, vertical magnetic field is carried out, both numerically and analytically. In contrast to previous investigations of upward-propagating waves (Zhugzhda and Dzhalilov: Astron. Astrophys. 112, 16, 1982a; Cally: Astrophys. J. 548, 473, 2001), this paper studies the downward propagation of waves from a low-β to high-β environment. A simple expression for the amplitude of the transmitted wave is compared with the numerical solution.  相似文献   

14.
In a recent paper “Head-on collision of electron acoustic solitary waves in a plasma with nonextensive hot electrons” (Astrophys. Space Sci. 338:271–278, 2012) Eslami, Mottaghizadeh and Pakzad deal with the problem of the head-on collisions between two weakly nonlinear electron-acoustic solitary waves. Unfortunately, their treatment is deficient and leads to erroneous conclusions.  相似文献   

15.
This letter points out that the values of ‘critical-acceleration’ of MOND, and the ‘accelerated-expansion’ of the universe are just two of the fourteen strikingly equal values of accelerations recurring in different physical situations. Some of them could be explained by a new law of equality of potential-energy and energy-of-mass of reasonably-independent systems (Tank in Astrophys. Space Sci. 330:203–205, 2010; Tank in Adv. Stud. Theor. Phys. 5:45–55, 2011). This new conservation-law, of equality of potential-energy, energy-of-mass and ‘kinetic-energy’ may be a clue to understand MOND, and the ‘accelerated-expansion’ of the universe. Alternative expressions for the cosmological red-shift, the ‘critical-acceleration’ of MOND and Newton’s law of universal gravitation are also presented for comparison of three different accelerations.  相似文献   

16.
Field equations in the presence of cosmic string source are obtained in a scalar tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124, 925 (1961)) with the aid of a five-dimensional Kaluza–Klein metric. An exact string cosmological model is presented which represents a five-dimensional Reddy string (Astrophys. Space Sci. 286, 2003b) in Brans–Dicke theory. Some physical properties of the model are also discussed  相似文献   

17.
A fully and coherent relativistic fluid model derived from the covariant formulation of relativistic fluid equations is used to study ion-acoustic solitary waves in a fully relativistic ion-electron-positron plasma. This approach has the characteristic to be consistent with the relativistic principle and consequently leads to a more general set of equations valid for fully relativistic plasmas with arbitrary Lorentz relativistic factor. Our results may be relevant to cosmic relativistic double- layers and relativistic plasma structures involving energetic plasma flows that may occur in space plasmas. Furthermore, they may complement and provide new insights into recently published results (G. Lu et al. in Astrophys. Space Sci., doi:, 2010).  相似文献   

18.
In a recent paper, published in Astrophys. Space Sci. (337:107, 2012) (hereafter paper ZZX) and entitled “On the triangular libration points in photogravitational restricted three-body problem with variable mass”, the authors study the location and stability of the generalized Lagrange libration points L 4 and L 5. However their study is flawed in two aspects. First they fail to write correctly the equations of motion of the variable mass problem. Second they attribute a variable mass to the third body of the restricted three-body model, a fact that is not compatible with the assumptions used in deriving the mathematical formulation of this model.  相似文献   

19.
Five-dimensional spherically symmetric space-time is considered in bimetric theory of gravitation formulated by Rosen (Gen. Rel. Grav. 4, 435, 1973) in the presence of cosmic string dust cloud. Exact cosmological models which represent geometric (Nambu) string, p-string (Takabayasi string) and Reddy string (Astrophys. Space Sci. 301, 2006) are obtained in the static and non-static cases. Some physical properties of the models are also discussed.  相似文献   

20.
We present dark energy models in an anisotropic Bianchi type-VI0 (B-VI0) space-time with a variable equation of state (EoS). The EoS for dark energy ω is found to be time dependent and its existing range for derived models is in good agreement with the recent observations of SNe Ia data (Knop et al. in Astrophys. J. 598:102 2003), SNe Ia data with CMBR anisotropy and galaxy clustering statistics (Tegmark et al. in Astrophys. J. 606:702, 2004b) and latest a combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift type Ia supernovae and galaxy clustering (Hinshaw et al. in Astrophys. J. Suppl. 180:225, 2009; Komatsu et al. in Astrophys. J. Suppl. 180:330, 2009). The cosmological constant Λ is found to be a positive decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results from recent supernovae Ia observations. The physical and geometric aspects of the models are also discussed in detail.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号