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1.
In this paper we present a detailed study of BCT Ist solution Tewari (Astrophys. Space Sci. 149:233, 1988) representing time dependent balls of perfect fluid with matter-radiation in general relativity. Assuming the life time of
quasar 107 years our model has initial mass≈108
M
Θ with an initial linear dimension≈1015 cm. Our model is radiating the energy at a constant rate i.e. L
∞=1047 ergs/sec with the gravitational red shift, z=0.44637. In this model we have 2GM(u)/c
2
R
S
(u))=0.3191 i.e. the model is horizon free. 相似文献
2.
Neeraj Pant 《Astrophysics and Space Science》2011,334(2):267-271
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 (0.3277≤K≤0.49), 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=0.3277 with X=−0.15, the maximum mass of the star comes out to be M=0.92M
Θ with radius r
b
≈17.15 km and the surface red shift Z
b
≈0.087187. It has been observed that under well behaved conditions this class of solutions gives us the mass of super dense
object within the range of white-dwarf. 相似文献
3.
Neeraj Pant 《Astrophysics and Space Science》2011,332(2):403-408
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
4.
Antonio Alfonso-Faus 《Astrophysics and Space Science》2009,321(1):69-72
It is shown that the usual choice of units obtained by taking G=c=ℏ=1, giving the Planck’s units of mass, length and time, introduces an artificial contradiction between cosmology and particle
physics: the lambda problem that we associate with ℏ. We note that the choice of ℏ=1 does not correspond to the scale of quantum physics. For this scale we prove that the correct value is ℏ≈1/10122, while the choice of ℏ=1 corresponds to the cosmological scale. This is due to the scale factor of 1061 that converts the Planck scale to the cosmological scale. By choosing the ratio G/c
3=constant=1, which includes the choice G=c=1, and the momentum conservation mc=constant, we preserve the derivation of the Einstein field equations from the action principle. Then the product Gm/c
2=r
g
, the gravitational radius of m, is constant. For a quantum black hole we prove that ℏ≈r
g
2≈(mc)2. We also prove that the product Λℏ is a general constant of order one, for any scale. The cosmological scale implies Λ≈ℏ≈1, while the Planck scale gives Λ≈1/ℏ≈10122. This explains the Λ problem. We get two scales: the cosmological quantum black hole (QBH), size ∼1028 cm, and the quantum black hole (qbh) that includes the fundamental particles scale, size ∼10−13 cm, as well as the Planck’ scale, size ∼10−33 cm.
相似文献
5.
We present a variety of well behaved classes of Charge Analogues of Tolman’s iv (1939). These solutions describe charged 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, however, the electric intensity is monotonically increasing in nature. These solutions give us
wide range of parameter for every positive value of n for which the solution is well behaved hence, suitable for modeling
of super dense stars. keeping in view of well behaved nature of these solutions, one new class of solutions is being studied
extensively. Moreover, this class of solutions gives us wide range of constant K (0.3≤K≤0.91) for which the solution is well behaved hence, suitable for modeling of super dense stars like Strange Quark stars,
Neutron stars and Pulsars. For this class of solutions the mass of a star is maximized with all degree of suitability, compatible
with Quark stars, Neutron stars and Pulsars. By assuming the surface density ρ
b
=2×1014 g/cm3 (like, Brecher and Caporaso in Nature 259:377, 1976), corresponding to K=0.30 with X=0.39, the resulting well behaved model has the mass M=2.12M
Θ, radius r
b
≈15.27 km and moment of inertia I=4.482×1045 g cm2; for K=0.4 with X=0.31, the resulting well behaved model has the mass M=1.80M
Θ, radius r
b
≈14.65 km and moment of inertia I=3.454×1045 g cm2; and corresponding to K=0.91 with X=0.135, the resulting well behaved model has the mass M=0.83M
Θ, radius r
b
≈11.84 km and moment of inertia I=0.991×1045 g cm2. For n=0 we rediscovered Pant et al. (in Astrophys. Space Sci. 333:161, 2011b) well behaved solution. These values of masses and moment of inertia are found to be consistent with other models of Neutron
stars and Pulsars available in the literature and are applicable for the Crab and the Vela Pulsars. 相似文献
6.
The focussing of gravitational radiation by the interior and exterior gravitational field of a Newtonian gravitational lens
is considered. A graphical method for determining the caustic structure of a Newtonian gravitational lens is presented and
the caustic structure of a solar type gravitational lens is discussed. Estimates of the amplitude magnification in the caustic
region indicate that waves with frequencies less than a critical cutoff frequency ω
c
are not amplified significantly. For a lens of massM this cutoff frequency is ω
c
≈(10-1πM)-1; for the Sun ω
c
≈104s-1.
Work supported in part by National Science Foundation Grant PHY78-05368. 相似文献
7.
A new class of charged super-dense star models is obtained by using an electric intensity, which involves a parameter, K. The metric describing the model shares its metric potential g 44 with that of Durgapal’s fourth solution (J. Phys. A, Math. Gen. 15:2637, 1982). The pressure-free surface is kept at the density ρ b =2×1014 g/cm3 and joins smoothly with the Reissner-Nordstrom solution. The charge analogues are well-behaved for a wide range, 0≤K≤59, with the optimum value of X=0.264 i.e. the pressure, density, pressure–density ratio and velocity of sound are monotonically decreasing and the electric intensity is monotonically increasing in nature for the given range of the parameter K. The maximum mass and the corresponding radius occupied by the neutral solution are 4.22M Θ and 20 km, respectively for X=0.264. For the charged solution, the maximum mass and radius are defined by the expressions M≈(0.0059K+4.22)M Θ and r b ≈−0.021464K+20 km respectively. 相似文献
8.
We present a new spherically symmetric solution of the general relativistic field equations in isotropic coordinates. The
solution is having positive finite central pressure and positive finite central density. The ratio of pressure and density
is less than one and casualty condition is obeyed at the centre. Further, the outmarch of pressure, density and pressure-density
ratio, and the ratio of sound speed to light is monotonically decreasing. The solution is well behaved for all the values
of u lying in the range 0<u≤.186. The central red shift and surface red shift are positive and monotonically decreasing. Further, we have constructed
a neutron star model with all degree of suitability and by assuming the surface density ρ
b
=2×1014 g/cm3. The maximum mass of the Neutron star comes out to be M=1.591 M
Θ with radius R
b
≈12.685 km. The most striking feature of the solution is that the solution not only well behaved but also having one of the
simplest expressions so far known well behaved solutions. Moreover, the good matching of our results for Vela pulsars show
the robustness of our model. 相似文献
9.
Xingting Pu 《Astrophysics and Space Science》2012,337(1):331-334
Using a homogenous sample of 1962 quasars with redshift 3.0≤z≲4.5 drawn from the Sloan Digital Sky Survey (SDSS), we study the relationships between radio loudness, virial black hole
(BH) mass and Eddington ratio (accretion rate relative to the Eddington limit). For the radio-detected objects, we find a
significant (>99.5 per cent) anticorrelation between radio loudness R parameter and BH mass, consistent with previous studies of low-redshift radio-loud quasars. The truly radio-loud quasars
(R>30) are found to be confined to M
BH≲1010 M⊙ within our sample. We also find that R is only weakly correlated with Eddington ratio L
bol/L
Edd. Combined with previous results on the low-redshift R−L
bol/L
Edd relation, this result indicates no strong L
bol/L
Edd dependence of R at L
bol/L
Edd≳10−2. On the other hand, the large scatter in these relationships suggests that other physical properties such as BH spin and
quasar clustering must also play an important role in quasar radio emission. 相似文献
10.
A dm-radio emission with fiber bursts observed on 11 July 2005 was analyzed using wavelet filtration and spectral methods.
In filtered radio spectra we found structures with different characteristic period P and frequency drift FD: i) fiber substructures (composed of dot emissions) with P
1≈ 0.5 s, FD1=− 87 MHz s−1 on average, ii) fiber structures with P
2≈1.9 s, and iii) drifting structures with P
3≈81.4 s, FD2=− 8.7, + 98.5, and − 21.8 MHz s−1. In the wavelet spectra we recognized patterns having the form of tadpoles. They were detected with the same characteristic
periods P as found for the filtered structures. The frequency drift of the tadpole heads is found to be equal to the frequency drift
of some groups of fibers for the long-period wavelet tadpoles (P
3) and to the frequency drift of individual fibers for the short-period tadpoles (P
2). Considering these wavelet tadpoles as signatures of propagating magnetoacoustic wave trains, the results indicate the presence
of several wave trains in the fibers’ source. While the long-period wave trains trigger or modulate a whole group of fibers,
the short-period ones look like being connected with individual fiber bursts. This result supports the model of fibers based
on magnetoacoustic waves. Using a density model of the solar atmosphere we derived the velocities of the magnetoacoustic waves,
107 and 562 km s−1, and setting them equal to the Alfvén ones we estimated the magnetic field in the source of fiber bursts as 10.7 and 47.8 G. 相似文献
11.
By using rather conservative estimates based on the simplest polar cap model, we search the ATNF Pulsar Catalogue for strongly
magnetized stars that could accelerate relativistic protons up to the curvature pion production threshold. The best candidate
turns out to be the 16 ms pulsar J0537-6910, but the corresponding characteristic parameter χ=a/m
p
is yet too small to give origin to observable signals. We show that, for pulsars with period P≈1 ms, a surface polar magnetic field B≈1012 G is required in order to induce detectable curvature pion radiation from accelerated protons in the magnetosphere. Some
other emission processes are also considered. 相似文献
12.
First ever closed form solution for charged fluid sphere expressed by a space time with its hypersurfaces t= constant as spheroid is obtained for the case 0<K<1. The same is utilized to construct a superdense star with surface density 2×1014 gm/cm3. The star is seen to satisfy the reality and causality conditions for 0<K≤0.045 and possesses maximum mass and radius to be 0.065216M
Θ and 1.137496 km respectively. Moreover the interior of the star satisfy strong energy condition. However in the absence of
the causality condition, the reality conditions are valid for a wider range 0<K≤0.13. The maximum mass and radius for the later case are 1.296798M
Θ and 2.6107 km respectively for the strong energy condition, while the said parameters for the weak energy condition read
as 1.546269M
Θ and 2.590062 km respectively. 相似文献
13.
A model for the high-frequency (20–2400 Hz) quasi-periodic oscillations (QPOs) of magnetars based on the representation of
coronal magnetic loops as equivalent electric RLC circuits is proposed. The observed periods of the QPOs and their high Q-factor (Q ≈ 104–105) are explained. It follows from the model that the QPOs can be excited not only in the tail of a flare but also before the
main pulse. The parameters of the QPO source at the “ringing tail” stage of the flare from SGR 1806–20 on December 27, 2004,
have been estimated: electric current I ≈ 3 × 1019 A, minimum magnetic field strength B
min ≈ 1013 G, and electron density n ≈ 2 × 1016 cm−3. 相似文献
14.
We present the results of our infrared observations of WR 140 (=V1687 Cyg) in 2001–2010. Analysis of the observations has
shown that the J brightness at maximum increased near the periastron by about 0
m
.3; the M brightness increased by ∼2
m
in less than 50 days. The minimum J brightness and the minimum L and M brightnesses were observed 550–600 and 1300–1400 days after the maximum, respectively. The JHKLM brightness minimum was observed in the range of orbital phases 0.7–0.9. The parameters of the primary O5 component of the
binary have been estimated to be the following: R(O5) ≈ 24.7R
⊙, L(O5) ≈ 8 × 105
L
⊙, and M
bol(O5) ≈ −10
m
. At the infrared brightness minimum, T
g ∼ 820–880 K, R
g ≈ 2.6 × 105
R
⊙, the optical depth of the shell at 3.5 μm is ∼5.3 × 10−6, and its mass is ≈1.4 × 10−8
M
⊙. At the maximum, the corresponding parameters are ∼1300 K, 8.6 × 104
R
⊙, ∼2 × 10−4, and ∼6 × 10−8
M
⊙; the mean rate of dust inflow (condensation) into the dust structure is ∼3.3 × 10−8
M
⊙ yr−1. The mean escape velocity of the shell from the heating source is ∼103 km s−1 and the mean dispersal rate of the shell is ∼1.1 × 10−8
M
⊙ yr−1. 相似文献
15.
Based on the methods of coronal seismology, we have investigated the ten-second quasi-periodic pulsations of the optical flare
emission from the active red dwarf EQ Peg B detected with the William Herschel Telescope on La Palma. We propose and analyze
a model in which they could be produced by sausage oscillations of a coronal flare loop. The amplitude and phase relations
between the displacement components of the radial oscillations and the conditions for their excitation in loops with footpoints
frozen into the photosphere are considered. The temperature (≈6 × 107 K), plasma density (≈2.7 × 1011 cm−3), and magnetic field strength (≈540 G) in the region of energy release have been determined. Our estimate of the flare loop
length (≈0.4R
⋆) provides evidence for the existence of extended coronae on red dwarf stars. 相似文献
16.
Rajmal Jain Arun Kumar Awasthi Arvind Singh Rajpurohit Markus J. Aschwanden 《Solar physics》2011,270(1):137-149
We report solar flare plasma to be multi-thermal in nature based on the theoretical model and study of the energy-dependent
timing of thermal emission in ten M-class flares. We employ high-resolution X-ray spectra observed by the Si detector of the
“Solar X-ray Spectrometer” (SOXS). The SOXS onboard the Indian GSAT-2 spacecraft was launched by the GSLV-D2 rocket on 8 May
2003. Firstly we model the spectral evolution of the X-ray line and continuum emission flux F(ε) from the flare by integrating a series of isothermal plasma flux. We find that the multi-temperature integrated flux F(ε) is a power-law function of ε with a spectral index (γ)≈−4.65. Next, based on spectral-temporal evolution of the flares we find that the emission in the energy range E=4 – 15 keV is dominated by temperatures of T=12 – 50 MK, while the multi-thermal power-law DEM index (δ) varies in the range of −4.4 and −5.7. The temporal evolution of the X-ray flux F(ε,t) assuming a multi-temperature plasma governed by thermal conduction cooling reveals that the temperature-dependent cooling
time varies between 296 and 4640 s and the electron density (n
e) varies in the range of n
e=(1.77 – 29.3)×1010 cm−3. Employing temporal evolution technique in the current study as an alternative method for separating thermal from nonthermal
components in the energy spectra, we measure the break-energy point, ranging between 14 and 21±1.0 keV. 相似文献
17.
A class of well behaved charged superdense star models of embedding class one is obtained by taking perfect fluid to be interior
matter. In the process we come across the models for white dwarf, quark and neutron stars. Maximum mass of the star of this
class is found to be 6.716998M
Θ with its radius is 18.92112 Km. In the absence of charge the models reduce to Schwarzchild’s interior model with constant
density. 相似文献
18.
We obtain a new class of charged super-dense star models after prescribing particular forms of the metric potential g
44 and electric intensity. The metric describing the superdense stars joins smoothly with the Reissner-Nordstrom metric at the
pressure free boundary. The interior of the stars possess there energy density, pressure, pressure-density ratio and velocity
of sound to be monotonically decreasing towards the pressure free interface. In view of the surface density 2×1014 g/cm3, the heaviest star occupies a mass 5.6996 M
⊙ with its radius 17.0960 km. The red shift at the centre and boundary are found to be 3.5120 and 1.1268 respectively. 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). 相似文献
19.
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
20.
We report very high temporal and spectral resolution interferometric observations of some unusual solar radio bursts near
1420 MHz. These bursts were observed on 13 September 2005, 22 minutes after the peak of a GOES class X flare from the NOAA
region 10808. Our observations show 11 episodes of narrow-band intermittent emission within a span of ≈ 8 s. Each episode
shows a heavily frequency-modulated band of emission with a spectral slope of about −245.5 MHz s−1, comprising up to 8 individual blobs of emission and lasts for 10 – 15 ms. The blobs themselves have a spectral slope of
≈ 0 MHz s−1, are ≈ 200 – 250 kHz wide, appear every ≈ 400 kHz and last for ≈ 4 – 5 ms. These bursts show brightness temperatures in the
range 1012 K, which suggests a coherent emission mechanism. We believe these are the first high temporal and spectral resolution interferometric
observations of such rapid and narrow-bandwidth solar bursts close to 1420 MHz and present an analysis of their temporal and
spectral characteristics. 相似文献