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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.
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
3.
Clovis Jacinto de Matos 《Astrophysics and Space Science》2012,337(1):353-354
The phenomenological nature of a new gravitational type interaction between two different bodies derived from Verlinde’s entropic
approach to gravitation in combination with Sorkin’s definition of Universe’s quantum information content, is investigated.
Assuming that the energy stored in this entropic gravitational field is dissipated under the form of gravitational waves and
that the Heisenberg principle holds for this system, one calculates a possible value for an absolute minimum time scale in
nature
t = \frac1516 \fracL1/2(h/2p) Gc4 ~ 9.27×10-105\tau=\frac{15}{16} \frac{\Lambda^{1/2}\hbar G}{c^{4}}\sim9.27\times10^{-105} seconds, which is much smaller than the Planck time t
P
=(ħG/c
5)1/2∼5.38×10−44 seconds. This appears together with an absolute possible maximum value for Newtonian gravitational forces generated by matter
Fg=\frac3230\fracc7L (h/2p) G2 ~ 3.84×10165F_{g}=\frac{32}{30}\frac{c^{7}}{\Lambda \hbar G^{2}}\sim 3.84\times 10^{165} Newtons, which is much higher than the gravitational field between two Planck masses separated by the Planck length F
gP
=c
4/G∼1.21×1044 Newtons. 相似文献
4.
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
5.
We study the effects of a non-singular gravitational potential on satellite orbits by deriving the corresponding time rates
of change of its orbital elements. This is achieved by expanding the non-singular potential into power series up to second
order. This series contains three terms, the first been the Newtonian potential and the other two, here R
1 (first order term) and R
2 (second order term), express deviations of the singular potential from the Newtonian. These deviations from the Newtonian
potential are taken as disturbing potential terms in the Lagrange planetary equations that provide the time rates of change
of the orbital elements of a satellite in a non-singular gravitational field. We split these effects into secular, low and
high frequency components and we evaluate them numerically using the low Earth orbiting mission Gravity Recovery and Climate
Experiment (GRACE). We show that the secular effect of the second-order disturbing term R
2 on the perigee and the mean anomaly are 4″.307×10−9/a, and −2″.533×10−15/a, respectively. These effects are far too small and most likely cannot easily be observed with today’s technology. Numerical
evaluation of the low and high frequency effects of the disturbing term R
2 on low Earth orbiters like GRACE are very small and undetectable by current observational means. 相似文献
6.
We study the anomalous flux ratio which is observed in some four-image lens systems, where the source lies close to a fold
caustic. In this case two of the images are close to the critical curve and their flux ratio should be equal to unity, instead
in several cases the observed value differs significantly. The most plausible solution is to invoke the presence of substructures,
as for instance predicted by the Cold Dark Matter scenario, located near the two images. In particular, we analyze the two
fold lens systems PG1115+080 and B1555+375, for which there are not yet satisfactory models which explain the observed anomalous
flux ratios. We add to a smooth lens model, which reproduces well the positions of the images but not the anomalous fluxes,
one or two substructures described as singular isothermal spheres. For PG1115+080 we consider a smooth model with the influence
of the group of galaxies described by a SIS and a substructure with mass ∼105
M
⊙ as well as a smooth model with an external shear and one substructure with mass ∼108
M
⊙. For B1555+375 either a strong external shear or two substructures with mass ∼107
M
⊙ reproduce the data quite well. 相似文献
7.
Naveen Bijalwan 《Astrophysics and Space Science》2011,334(1):139-143
A most general exact solution to the Einstein-Maxwell equations for static charged perfect fluid is sought in terms of pressure.
Subsequently, metrics (e
λ
and e
υ
), matter density and electric intensity are expressible in terms of pressure. Consequently, Pressure is found to be an invertible
arbitrary function of ω(=c
1+c
2
r
2), where c
1 and c
2(≠0) are arbitrary constants, and r is the radius of star, i.e. p=p(ω). We present a general solution for charged pressure fluid in terms for ω. We list and discuss some old and new solutions which fall in this category. 相似文献
8.
The stability of strange dwarfs for quark cores with M
0core
/M
⨀ = 10−4, has been studied by calculating, in each individual case, a series of strange dwarfs with configurations in which 5 ⋅ 10−4, 10−3, 5 ⋅ 10−3, 10−2, 1.31 ⋅ 10−2, 1.6 ⋅ 10−2, 1.7 ⋅ 10−2, 2 ⋅ 10−2, ranges from the values in white dwarfs to ρ
drip
= 4.3 ⋅ 1011 g/cm3, at which free neutrons are produced in the crust. For the series with M
0core
/M
⨀ < 0.0131, stability is lost when ρ
tr
< ρ
drip
. For the series with M
0core
/M
⨀ > 0.0131, the equality ρ
tr
= ρ
drip
is reached before the strange dwarf attains its maximum mass. Although the frequency of the radial pulsations in the fundamental
mode obeys ω02 > 0 for these configurations, they are unstable with respect to transitions into a strange star state with the same total
number of baryons and a radius on the order of that of neutron stars. An energy on the order of the energy in a supernova
explosion is released during these transitions. It is shown that the gravitational red shift of white and strange dwarfs are
substantially different for low and limiting (high) masses. 相似文献
9.
In this paper we present a new class of nonsingular solutions representing time dependent balls of perfect fluid with matter-radiation
in general relativity. The solution of the class is suitable for interior modeling of a quasar i.e. a massive radiating star.
The interior solution is matched with a zero pressure Vaidya metric. From this solution we constructed a quasar model by assuming
the life time of the quasar of ≈107 year. We obtained a mass of the quasar of ≈109 M
θ
, linear dimension ≈1017 km and a rate of emission L
∞≈1047 erg/s. 相似文献
10.
V. V. Bobylev 《Astronomy Letters》2010,36(9):634-644
We analyze the three-dimensional kinematics of about 82 000 Tycho-2 stars belonging to the red giant clump (RGC). First, based
on all of the currently available data, we have determined new, most probable components of the residual rotation vector of
the optical realization of the ICRS/HIPPARCOS system relative to an inertial frame of reference, (ω
x
, ω
y
, ω
z
) = (−0.11, 0.24, −0.52) ± (0.14, 0.10, 0.16) mas yr−1. The stellar proper motions in the form μα cos δ have then be corrected by applying the correction ω
z
= −0.52 mas yr−1. We show that, apart from their involvement in the general Galactic rotation described by the Oort constants A = 15.82 ± 0.21 km s−1 kpc−1 and B = −10.87 ± 0.15 km s−1 kpc−1, the RGC stars have kinematic peculiarities in the Galactic yz plane related to the kinematics of the warped stellar-gaseous Galactic disk. We show that the parameters of the linear Ogorodnikov-Milne
model that describe the kinematics of RGC stars in the zx plane do not differ significantly from zero. The situation in the yz plane is different. For example, the component of the solid-body rotation vector of the local solar neighborhood around the
Galactic x axis is M
32− = −2.6 ± 0.2 km s−1 kpc−1. Two parameters of the deformation tensor in this plane, namely M
23+ = 1.0 ± 0.2 km s−1 kpc−1 and M
33 − M
22 = −1.3 ± 0.4 km s−1 kpc−1, also differ significantly from zero. On the whole, the kinematics of the warped stellar-gaseous Galactic disk in the local
solar neighborhood can be described as a rotation around the Galactic x axis (close to the line of nodes of this structure) with an angular velocity −3.1 ± 0.5 km s−1 kpc−1 ≤ ΩW ≤ −4.4 ± 0.5 km s−1 kpc−1. 相似文献
11.
Corrado Massa 《Astrophysics and Space Science》2006,305(4):377-384
Quantum theory in Robertson – Walker spacetime suggests the existence of a minimal energy ε of the order of 10−45 erg. Reasonable forms for ε give the expansion factor R=R(t)(t= the cosmic time) with no need of gravitational field equations.Einstein's theory should be modified in gravitational fields of strength less than ε c/ħ ∼ 10−8 cm/s2 where c is the speed of light and ħ is the reduced Planck constant. The cosmological term λ is expected to decrease as the universe expands.In the Appendix, ε is derived from a big bang – big crunch Newtonian cosmology. 相似文献
12.
We semi-quantitatively calculate the distribution of energy in frequency and angle emitted from a sheet of charges that are moving out relativistically along dipolar magnetic field lines originating near the magnetic polar caps of a rotating neutron star. The angular distribution is conical with the angle of maximum intensity varying with frequency as –1/4 for
c
2
c
/(R
M
2), whereRM is the initial angular radius of the charge sheet at the surface of the star of radiusR. At higher frequencies the width of the angular cone remains constant. The radiation is linearly polarized with the polarization vector in the plane of the line of sight and the magnetic axis. A sheet of uniform charge density and finite thickness has a frequency spectrum that varies from –3/2 to –4 for
c
and
c
, respectively. These features are in good general agreement with the observed characteristics of the intensity, pulse shape, and frequency spectrum of the radio pulses from pulsars.Operated by Associated Universities, Inc., under contract with the National Science Foundation. 相似文献
13.
We analyse the dark energy problem using observational H(z) data plus the curvature constraint given by WMAP. After a non-parametric
statistical study covering the most probable range of Ω
m0 and H
0 from different combination of data, we investigate the possibility of having the dark energy EoS parameter ω
x
≠−1. In order to keep strict flatness (1% of deviation from Ω=1), our results point out this is the case for 0.20≲Ω
m0≲0.23 and H
0≈67 km/s/Mpc, with ω
x
≈−0.55. However, if we admit a 10% deviation from the flatness condition, ω
x
may have any value in the range [−1.2,−0.5] for 0.20≲Ω
m0≲0.35 and 67≲H
0≲74 km/s/Mpc. 相似文献
14.
Veniamin Berezinsky 《Astrophysics and Space Science》2007,309(1-4):453-463
Propagation of UHE protons through CMB radiation leaves the imprint on energy spectrum in the form of Greisen–Zatsepin–Kuzmin
(GZK) cutoff, bump (pile-up protons) and dip. The dip is a feature in energy range 1×1018–4×1019 eV, caused by electron-positron pair production on CMB photons. Calculated for power-law generation spectrum with index
γ
g
=2.7, the shape of the dip is confirmed with high accuracy by data of Akeno—AGASA, HiRes, Yakutsk and Fly’s Eye detectors.
The predicted shape of the dip is robust: it is valid for the rectilinear and diffusive propagation, for different discretenesses
in the source distribution, for local source overdensity and deficit etc. This property of the dip allows us to use it for
energy calibration of the detectors. The energy shift λ for each detector is determined by minimum χ
2 in comparison of observed and calculated dip. After this energy calibration the absolute fluxes, measured by AGASA, HiRes
and Yakutsk detectors remarkably coincide in energy region 1×1018–1×1020 eV. Below the characteristic energy E
c
≈1×1018 eV the spectrum of the dip flattens for both diffusive and rectilinear propagation, and more steep galactic spectrum becomes
dominant at E<E
c
. The energy of transition E
tr<E
c
approximately coincides with the position of the second knee E
2kn
, observed in the cosmic ray spectrum. The dip-induced transition from galactic to extragalactic cosmic rays at the second
knee is compared with traditional model of transition at ankle, the feature observed at energy ∼1×1019 eV.
相似文献
15.
M. Dersarkissian 《Astrophysics and Space Science》1986,126(2):409-412
When cosmic quantum mechanics is applied to a double galaxy, the result is mass limits in order for the two galaxies to form a quantum binary system. For a non-relativistic theory (based on the Schrödinger wave equation), the mass limits are: (m
g)max 1012
M
and (m
g)min 1010
M
. One possible consequence appears to be a Newtonian gravitational constant that varies with cosmic time, with its value larger in the cosmic past. 相似文献
16.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2010,327(1):111-115
We investigate five-dimensional Brans–Dicke cosmology with spacetime described by the homogeneous, anisotropic and flat spacetime
with the topology M
1×R
3×S
1 where S
1 is taken in the form of a circle. We conjecture throughout this letter that the extra-dimension compactifies as the visible
dimensions expand like b(t)≈a
−1(t) and that the non-minimal coupling between the scalar field and the matter is of the form f(φ)∝
φ
2. The model gives rise to a transition from a decelerated epoch to an accelerated epoch for large values of the Brans–Dicke
parameter ω. The model predicts crossing of the phantom divided barrier unless the universe is governed by a growing matter field. 相似文献
17.
Naveen Bijalwan 《Astrophysics and Space Science》2011,336(2):413-418
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
18.
We investigate the influence of the following parameters on the crust properties of strange stars: the strange quark mass
(m
s), the strong coupling constant (αc) and the vacuum energy density (B). It is found that the mass density at the crust base of strange stars cannot reach the neutron drip density. For a conventional
parameter set of m
s=200 MeV, B
1/4 = 145 MeV and αc = 0.3, the maximum density at the crust base of a typical strange star is only 5.5 × 1010 gcm-3, and correspondingly the maximum crust mass is 1.4 ×10-6 M⊙. Subsequently, we present the thermal structure and the cooling behavior of strange stars with crusts of different thickness,
and under different diquark pairing gaps. Our work might provide important clues for distinguishing strange stars from neutron
stars. 相似文献
19.
Yu. A. Fadeyev 《Astronomy Letters》2011,37(6):403-413
Instability of population I (X = 0.7, Z = 0.02) massive stars against radial oscillations during the post-main-sequence gravitational contraction of the helium core
is investigated. Initial stellar masses are in the range 65M
⊙ ≤ M
ZAMS ≤ 90M
⊙. In hydrodynamic computations of self-exciting stellar oscillations we assumed that energy transfer in the envelope of the
pulsating star is due to radiative heat conduction and convection. The convective heat transfer was treated in the framework
of the theory of time-dependent turbulent convection. During evolutionary expansion of outer layers after hydrogen exhaustion
in the stellar core the star is shown to be unstable against radial oscillations while its effective temperature is T
eff > 6700 K for M
ZAMS = 65M
⊙ and T
eff > 7200 K for M
ZAMS = 90M
⊙. Pulsational instability is due to the κ-mechanism in helium ionization zones and at lower effective temperature oscillations decay because of significantly increasing
convection. The upper limit of the period of radial pulsations on this stage of evolution does not exceed ≈200 day. Radial
oscillations of the hypergiant resume during evolutionary contraction of outer layers when the effective temperature is T
eff > 7300 K for M
ZAMS = 65M
⊙ and T
eff > 7600 K for M
ZAMS = 90M
⊙. Initially radial oscillations are due to instability of the first overtone and transition to fundamental mode pulsations
takes place at higher effective temperatures (T
eff > 7700 K for M
ZAMS = 65M
⊙ and T
eff > 8200 K for M
ZAMS = 90M
⊙). The upper limit of the period of radial oscillations of evolving blueward yellow hypergiants does not exceed ≈130 day.
Thus, yellow hypergiants are stable against radial stellar pulsations during the major part of their evolutionary stage. 相似文献
20.
In this paper we have investigated the beat wave excitation of an ion-acoustic wave at the difference frequency of two kinetic
(or shear) Alfvén waves propagating in a magnetized plasma with β<1 (β=8π
n
e0
T
e/B
0
2
, where n
e0 is the unperturbed electron number density, T
e is the electron temperature, and B
0 is the external magnetic field). On account of the interaction between two kinetic Alfvén waves of frequencies ω
1 and ω
2, the ponderomotive force at the difference frequency ω
1−ω
2 leads to the generation of an ion-acoustic wave. Also because of the filamentation of the Alfvén waves, magnetic-field-aligned
density dips are observed. In this paper we propose that the ion-acoustic wave generated by this mechanism may be one of the
possible mechanisms for the heating and acceleration of solar wind particles. 相似文献