共查询到20条相似文献，搜索用时 31 毫秒
1.
S. I. Grachev 《Astrophysics》2007,50(4):515-524
A new method is proposed to account for multiple scattering by electrons in calculations of the correlation functions describing
the angular fluctuations in the cosmic microwave background radiation (CMBR). The apparatus of the theory of radiative transport
with Rayleigh scattering is used. The problem is reduced to solving an integral equation for the vector source function (dependent
only on time), along with differential equations for the other quantities (scalar potentials, baryon velocities, etc.) which
show up in the problem. The quantities which describe the angular fluctuations in the CMBR (in the temperature and in the
polarization) are then calculated by integrating the vector source function along the line of sight. As an illustration, the
correlation functions and power spectra are calculated for the case where the fluctuations are produced by some initial gaussian
perturbations of the CMBR.
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Translated from Astrofizika, Vol. 50, No. 4, pp. 621–631 (November 2007). 相似文献
2.
A. K. Verma 《Astrophysics and Space Science》2009,321(1):73-77
This paper focuses attention on a qualitative analysis of the evolution of two-fluid flat FRW cosmological models.In the first
model one of the fluid represents matter content of the universe comoving with respect to the another fluid that is the cosmic
microwave background radiation (CMBR), these two fluids are interacting.The first model is most relevant to describe the scenario
before the recombination epoch when matter and radiation were in an interactive phase and the photons was bound to electron
through Thomson scattering. The second model describe two noninteracting fluids where the matter is comoving to the space-time
coordinates and the CMBR is moving axially, relative to the matter thus modeling the relative velocity between galaxies and
the CMBR (Phys. Rev. Lett. 39:898–901, 1977). This model portray the cosmic evolution in the postrecombination epoch when the two-fluid are noninteracting.In this epoch
the photons got themselves free to form the CMBR being observed presently.
相似文献
3.
A study of the slowly rotating cosmological universe filled with viscous fluid has been made by assuming the matter angular
velocity Ω is proportional to the metric angular velocity Ω and the Universe is expanding under the Hubble's law. The physical
properties of the solutions obtained are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Robert J. Nemiroff 《Astrophysics and Space Science》1998,259(3):309-315
The density of stars and MACHOs in the universe could theoretically be determined or limited by simultaneous measurements
of compact sources by well separated observers. A gravitational lens effect would be expected to create a slight differential
amplification between the observers detectable with sufficiently sensitive relative photometry: 'lensing parallax'. When applied
to expanding fireballs such as those from GRBs and supernovae, the mass of the lens can be indicated by the end of lensing
parallax, when the angular size of the source becomes much greater than the angular size of the Einstein ring of the lens.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
Arbab I.Arbab 《中国天文和天体物理学报》2003,3(2):113-118
Exact solutions for a model with variable G,A and bulk viscosity are obtained,Inflationary solutions with constant(de Sitter-type )and variable energy density are found.An expanding anisotropic universe is found to isotropize during its expansion but a static universe cannot isotropize.The gravitational constant is found to increase with time and the cosmological constant decreases with time as A∝t^-2。 相似文献
6.
The exact closed-form mathematical solution for Schwarzschild black-hole fed by the Cosmic Micro-wave Background Radiance (CMBR) is obtained analytically. This unique solution holds for both growth (evolution) and decay, which are bifurcated by the critical initial mass, which depends on the temperature of CMBR. Results are presented to illustrate this solution in terms of decay/growth of black-hole, and the variation of rate of growth/decay with CMBR. 相似文献
7.
The Kepler problem is studied in a space with the Friedmann-Lemaitre-Robertson-Walker metrics of the expanding universe. Cosmic evolution leads to decreasing energy of particles, causing free particles to be captured in bound states, so that the evolution of the universe can be treated as a possible mechanism of the formation of galaxies and clusters of galaxies. The cosmological model is considered where the evolution of the universe plays the role usually inscribed to cold dark matter. 相似文献
8.
M. Melek 《Astrophysics and Space Science》2000,272(4):417-421
Limits on cosmic time scale variations of gravitational and cosmological `constants' are studied. The study is based on a
function which can measure the temporal variation of the magnitude of the gradient of any scalar field defined inside a medium
exposed to a gravitational field. The cosmic time dependent scalar fields are taken to be the gravitational and cosmological
`constants'. The medium; in which those scalar fields are defined; is taken to be the spatially perturbed Friedman-Robertson-Walker
(FRW) expanding universe.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
S. Hannestad 《Monthly notices of the Royal Astronomical Society》1999,309(2):556-560
Measurements of the cosmic microwave background radiation (CMBR) provide a powerful tool with which to measure the primary cosmological parameters. However, there is a large degree of parameter degeneracy in simultaneous measurements of the matter density, Ωm , and the Hubble parameter, H 0 . In the present paper we use the currently available CMBR data together with measurements of the cosmological baryon-to-photon ratio, η , from big bang nucleosynthesis, and the relative mass fraction of baryons in clusters to break the parameter degeneracy in measuring Ωm and H 0 . We find that present data are inconsistent with the standard Ω=1, matter-dominated model. Our analysis favours a medium-density universe with a rather low Hubble parameter. This is compatible with new measurements of Type Ia supernovae, and the joint estimate of the two parameters is and . We stress that the upper bound on the Hubble parameter is likely to be much more uncertain than indicated here, because of the limited number of free parameters in our analysis. 相似文献
10.
E. A. Evangelidis 《Astrophysics and Space Science》1981,74(1):207-210
The equations of motion are derived for a differentially rotating system, and the paper demonstrates the existence of a force term due to coupling of the angular momentum with the gradient of the angular frequency. Translation of the system of reference to the Local Standard of Rest (LSR) shows that the LSR executes a radial oscillatory motion as a necessary consequence of the coupling mentioned above. This mechanism could well provide the theoretical background for expanding galaxies without resorting to a violent explosion in their centre — a mechanism for which the evidence is rather scanty. 相似文献
11.
The equations of motion governing the evolution of a collisionless gravitating system of particles in an expanding universe can be cast in a form which is almost independent of the cosmological density parameter, Ω, and the cosmological constant, Λ. The new equations are expressed in terms of a time variable τ=ln D , where D is the linear rate of growth of density fluctuations. The dependence on the density parameter is proportional to ε=Ω−0.2 −1 times the difference between the peculiar velocity (with respect to τ) of particles and the gravity field (minus the gradient of the potential); or, before shell-crossing, times the sum of the density contrast and the velocity divergence. In a one-dimensional collapse or expansion, the equations are fully independent of Ω and Λ before shell crossing. In the general case, the effect of this weak Ω dependence is to enhance the rate of evolution of density perturbations in dense regions. In a flat universe with Λ7ne;0, this enhancement is less pronounced than in an open universe with Λ=0 and the same Ω. Using the spherical collapse model, we find that the increase of the rms density fluctuations in a low-Ω universe relative to that in a flat universe with the same linear normalization is ∼0.01ε(Ω)〈δ3 〉, where δ is the density field in the flat universe. The equations predict that the smooth average velocity field scales like Ω0.6 , while the local velocity dispersion (rms value) scales, approximately, like Ω0.5 . High-resolution N -body simulations confirm these results and show that density fields, when smoothed on scales slightly larger than clusters, are insensitive to the cosmological model. Haloes in an open model simulation are more concentrated than haloes of the same M /Ω in a flat model simulation. 相似文献
12.
Klaus Maisinger M. P. Hobson A. N. Lasenby & Neil Turok 《Monthly notices of the Royal Astronomical Society》1998,297(2):531-535
Topological defect theories lead to non-Gaussian features on maps of fluctuations of the cosmic microwave background radiation (CMBR), which enable us to distinguish them from maps predicted by standard inflationary models. We have recently presented a maximum entropy method (MEM) which simultaneously deconvolves interferometer maps of CMBR fluctuations, and separates out foreground contaminants. By applying this method to simulated observations using a realistic ground-based interferometer, we demonstrate that it is possible to recover the prominent hotspots in the CMBR maps which delineate individual defects, even in the presence of a significant Galactic foreground. 相似文献
13.
Ramona Núñez-López Anton Lipovka Vladimir Avila-Reese 《Monthly notices of the Royal Astronomical Society》2006,369(4):2005-2012
Possible detection of signatures of structure formation at the end of the 'dark age' epoch ( z ∼ 40–20) is examined. We discuss the spectral–spatial fluctuations in the cosmic microwave background radiation (CMBR) temperature produced by elastic resonant scattering of CMBR photons on deuterated hydrogen (HD) molecules located in protostructures moving with peculiar velocity. Detailed chemical kinematic evolution of HD molecules in the expanding homogeneous medium is calculated. Then, the HD abundances are linked to protostructures at their maximum expansion, whose properties are estimated by using the top-hat spherical approach and the Λ cold dark matter (ΛCDM) cosmology. We find that the optical depths in the HD three lowest pure rotational lines for high-peak protohaloes at their maximum expansion are much higher than those in LiH molecule. The corresponding spectral–spatial fluctuation amplitudes, however, are probably too weak to be detected by current and forthcoming millimetre telescope facilities. We extend our estimates of spectral–spatial fluctuations to gas clouds inside collapsed CDM haloes by using results from a crude model of HD production in these clouds. The fluctuations for the highest peak CDM haloes at redshifts ∼20–30 could be detected in the future. Observations will be important to test model predictions of early structure formation in the Universe. 相似文献
14.
We discuss the behavior of density fluctuations in an expanding universe and show that these should lead to the early formation
of pregalactic hydrogen-helium stars of several hundred to several thousand solar masses. These stars flood the universe with
radiation having a color temperature ≳105 K; this terminates star formation but permits galaxy formation to continue. About 10−2 of the mass of the galaxies is converted into heavy elements by pregalactic nucleosynthesis, with an error factor of a few. 相似文献
15.
The measurement of the temperature of the cosmic microwave background radiation (CMBR) with the Far InfraRed Absolute Spectrophotometer (FIRAS) on the Cosmic Background Explorer (COBE) satellite gives a possibility for determination of all mutually related parameters of the ultrastable expansive nondecelerative Universe (ENU) with deviations smaller than 0.4%.The measurement of the large-scale anisotropy of the CMBR with the Differential Microwave Radiometers (DMR) on the COBE satellite allows us to determine the mass density of gravitationally bound systems of large-scale structures of the ENU. 相似文献
16.
M. Melek 《Astrophysics and Space Science》1995,228(1-2):327-330
The aim of this brief report is to find a lower limit of the Hubble parameter using the COBE's detected fluctuations in the temperature of the CMBR. 相似文献
17.
In this article we want to answer the cosmologically relevant question what, with some good semantic and physical reason, could be called the massM u of an infinitely extended, homogeneously matter‐filled and expanding universe. To answer this question we produce a space‐like sum of instantaneous cosmic energy depositions surrounding equally each spacepoint in the homogeneous universe. We calculate the added‐up instantaneous cosmic energy per volume around an arbitrary space point in the expanding universe. To carry out this sum we use as basic metrics an analogy to the inner Schwarzschild metric applied to stars, but this time applied to the spacepoint‐related universe. It is then shown that this leads to the added‐up proper energy within a sphere of a finite outer critical radius defining the point‐related infinity. As a surprise this radius turns out to be reciprocal to the square root of the prevailing average cosmic energy density. The equivalent mass of the universe can then also be calculated and, by the expression which is obtained here, shows a scaling with this critical radius of this universe, a virtue of the universe which was already often called for in earlier works by E. Mach, H. Thirring and F. Hoyle and others. This radius on the other hand can be shown to be nearly equal to the Schwarzschild radius of the so‐defined mass M u of the universe. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
18.
Kaiki Taro Inoue Kenji Tomita Naoshi Sugiyama 《Monthly notices of the Royal Astronomical Society》2000,314(4):L21-L25
The effect of a non-trivial topology on the temperature correlations of the cosmic microwave background (CMB) in a small compact hyperbolic universe with volume comparable to the cube of the curvature radius is investigated. Because the bulk of large-angle CMB fluctuations are produced at the late epoch in low-Ω0 models, the effect of a long-wavelength cut-off owing to the periodic structure does not lead to significant suppression of large-angle power as in compact flat models. The angular power spectra are consistent with COBE data for Ω0 0.1. 相似文献
19.
Dynamical parameters like average velocity dispersion and temperature profile of galaxy clusters are determined using the theory of quasi-equilibrium thermodynamics. The calculated results of velocity dispersion show a good agreement between theory and simulations with the results of velocity dispersion from Abdullah et al. An adaptive mesh refinement grid-based hybrid code has been used to carry out the simulations. Our results indicate that the average velocity dispersion profile of 20Abell galaxy clusters falls in the range of 500- 1000 km s-1and their temperature profile is of the order of 107to 108K calculated on the basis of kinetic theory. The data in the plot show a significant contribution from gravitating particles clustering together in the vicinity of the cluster center and beyond a certain region this velocity dies out and becomes dominated by the Hubble flow due to which all the galaxy clusters in an expanding universe participate in Hubble expansion. 相似文献
20.
汪定雄 《中国天文和天体物理学报》1999,(4)
对黑洞吸积盘内区温度的径向分布特征和演化特征作了详细的讨论．结果表明：（１）盘内区的温度并非随径向坐标ｒ单调减少,在接近盘的内边缘处有一个盘温的峰值环．在盘温的峰值环和盘的内边缘之间形成一个温度梯度很大的冷却区;（２）在盘吸积的过程中,盘内区温度的峰值和冷却区的平均温度梯度均随中心黑洞的无量纲角动量ａ的增加而单调增加,而金温峰值环半径和冷却区的径向宽度均随ａ的增加而单调减小;（３）盘的热辐射光度随ａ的增加而单调增加． 相似文献