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1.
The evolution of a perfect fluid perturbation is considered in the radiation dominated period and in the dust epoch. In the investigation we make use of the general formalism developed in previous papers.It turns out that the evolution tendency is predicted by the state of the cosmic background. The radiation dominated universe does not stimulate growing processes of the perturbation, whereas the dust dominated universe causes a growing tendency of small perfect fluid formations. The results of this work are in accordance with these obtained by the present writers in a previous work. 相似文献
2.
Walter Petry 《Astrophysics and Space Science》1997,250(2):297-311
In a previous paper the equations of small cosmological perturbations of a theory of gravitation in flat space-time are derived. They are applied to a homogeneous, isotropic, nonsingular cosmological model with radiation, matter and background field. At the beginning of the universe small spherically symmetric inhomogeneities on almost all scales can arise by instability. Later on the density contrast of dust grows exponentially during a short time epoch. The solution during this time period is given analytically. 相似文献
3.
T. X. Zhang 《Astrophysics and Space Science》2010,330(1):157-165
Modifying slightly the big bang theory, the author has recently developed a new cosmological model called black hole universe.
This new cosmological model is consistent with the Mach principle, Einsteinian general theory of relativity, and observations
of the universe. The origin, structure, evolution, and expansion of the black hole universe have been presented in the recent
sequence of American Astronomical Society (AAS) meetings and published recently in a scientific journal: Progress in Physics.
This paper explains the observed 2.725 K cosmic microwave background radiation of the black hole universe, which grew from
a star-like black hole with several solar masses through a supermassive black hole with billions of solar masses to the present
universe with hundred billion-trillions of solar masses. According to the black hole universe model, the observed cosmic microwave
background radiation can be explained as the black body radiation of the black hole universe, which can be considered as an
ideal black body. When a hot and dense star-like black hole accretes its ambient materials and merges with other black holes,
it expands and cools down. A governing equation that expresses the possible thermal history of the black hole universe is
derived from the Planck law of black body radiation and radiation energy conservation. The result obtained by solving the
governing equation indicates that the radiation temperature of the present universe can be ∼2.725 K if the universe originated
from a hot star-like black hole, and is therefore consistent with the observation of the cosmic microwave background radiation.
A smaller or younger black hole universe usually cools down faster. The characteristics of the original star-like or supermassive
black hole are not critical to the physical properties of the black hole universe at present, because matter and radiation
are mainly from the outside space, i.e., the mother universe. 相似文献
4.
Walter Petry 《Astrophysics and Space Science》1997,254(2):305-317
A nonsingular, homogeneous, isotropic cosmological model with cosmological constant in flat space-time theory of gravitation
is studied. The second law of thermodynamics yields a nonexpanding (nonstationary) universe without entropy production. At
the beginning of the universe radiation, matter and vacuum energy given by the cosmological constant are zero and then emerge
from gravitational energy. In the course of time the energy of radiation and matter decrease whereas the vacuum energy increases
forever. Light emitted from a distant galaxy loses energy on his way to the observer producing the observed redshift. The
velocity of light in the past is greater than the present one. This may explain superluminal velocities but only for large
redshifts. The sum of the density parameters of matter, radiation and vacuum energy is a little greater than one. All the
matter can be baryonic. There is no age problem of the universe.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
In the framework of a previously developed procedure the evolution of small spherically symmetric perturbations in a homogeneous R-W-F universe is analyzed. It turns out that the evolution tendency is mainly predicted by the state of the cosmic background. In the radiation dominated period the universe does not stimulate growing processes, a perturbation will be in a frozen state or it will diffuse. It is found that a dust dominated universe stimulates the perturbation masses to grow. The rate of this cosmic affected growing process is proportional to (R)–1/2 (R being the scale factor). Consequently almost all galaxies were formed at the beginning of the dust dominated era. 相似文献
6.
We consider a late closed universe of which scale factor is a power function of time using observational data from combined WMAP5+BAO+SN Ia dataset and WMAP5 dataset. The WMAP5 data give power-law exponent, α=1.01 agreeing with the previous study of H(z) data while combined data gives α=0.985. Considering a scalar field dark energy and dust fluid evolving in the power-law universe, we find field potential, field solution and equation of state parameters. Decaying from dark matter into dark energy is allowed in addition to the non-interaction case. Time scale characterizing domination of the kinematic expansion terms over the dust and curvature terms in the scalar field potential are found to be approximately 5.3 to 5.5 Gyr. The interaction affects in slightly lowering the height of scalar potential and slightly shifting potential curves rightwards to later time. Mass potential function of the interacting Lagrangian term is found to be exponentially decay function. 相似文献
7.
In this paper we present a class of solutions of Einstein's field equations describing two-fluid models of the universe in
a locally rotationally symmetric Bianchi type II space-time. In these models one fluid is the radiation distribution which
represents the cosmic microwave background and the other fluid is the perfect fluid representing the matter content of the
universe. It is found that both the fluids are comoving in the locally rotationally symmetric Bianchi type II space-time.
The behaviour of the radiation density, matter density, the ratio of the matter density to the radiation density and the pressure
has been discussed. A subclass of solutions is found to describe models of a spatially homogeneous and partially isotropic
universe evolving from a radiation dominated era to a pressure free matter dominated era.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Atreyee Biswas 《Astrophysics and Space Science》2018,363(10):203
The present work deals with irreversible thermodynamics of universe containing interacting dark fluids. Recent observational evidences reveal that the universe is dominated by two dark components-dark matter and dark energy. The interaction between them leads to spontaneous heat flow between the horizon and the fluid system and as a result the system will no longer be in thermal equilibrium. In this paper dark matter is chosen as pressureless dust while modified Chaplygin gas has been considered as dark energy. In two separate cases we have considered the universe to be bounded by apparent horizon and event horizon and the validity of generalized second law of thermodynamics in the context of irreversible thermodynamics has been studied for both the cases. 相似文献
9.
Jayant V. Narlikar Geoffrey Burbidge R. G. Vishwakarma 《Journal of Astrophysics and Astronomy》2007,28(2-3):67-99
In this paper we discuss the properties of the quasi-steady state cosmological model (QSSC) developed in 1993 in its role
as a cyclic model of the universe driven by a negative energy scalar field. We discuss the origin of such a scalar field in
the primary creation process first described by F. Hoyle & J. V. Narlikar forty years ago. It is shown that the creation processes
which take place in the nuclei of galaxies are closely linked to the high energy and explosive phenomena, which are commonly
observed in galaxies at all redshifts.
The cyclic nature of the universe provides a natural link between the places of origin of the microwave background radiation
(arising in hydrogen burning in stars), and the origin of the lightest nuclei (H, D, He3 and He4). It also allows us to relate the large scale cyclic properties of the universe to events taking place in the nuclei of galaxies.
Observational evidence shows that ejection of matter and energy from these centers in the form of compact objects, gas and
relativistic particles is responsible for the population of quasi-stellar objects (QSOs) and gamma-ray burst sources in the
universe.
In the later parts of the paper we briefly discuss the major unsolved problems of this integrated cosmological and cosmogonical
scheme — the understanding of the origin of the intrinsic redshifts, and the periodicities in the redshift distribution of
the QSOs. 相似文献
10.
《天文和天体物理学研究(英文版)》2016,(4)
On studying some new models of Robertson-Walker universes with a Brans-Dicke scalar field, it is found that most of these universes contain a dark energy like fluid which confirms the present scenario of the expansion of the universe. In one of the cases, the exact solution of the field equations gives a universe with a false vacuum, while in another it reduces to that of dust distribution in the Brans-Dicke cosmology when the cosmological constant is not in the picture. In one particular model it is found that the universe may undergo a Big Rip in the future, and thus it will be very interesting to investigate such models further. 相似文献
11.
The solution of three new interesting studies,a rotating anisotropic twofluid universe coupled with radiation and a scalar field,are studied here,where the anisotropic pressure is generated by the presence of two non-interacting perfect fluids which are in relative motion with respect to each other.In this problem,special discussion is made of the physically interesting class of models in which one fluid is a perfect comoving radiative fluid which is taken to model the cosmic microwave background and the se... 相似文献
12.
The bounds for the energy change rate of a Maxwell field in the outer space of a rotating black hole, calculated by de Vries (1994) and de Vries (1995), enable us to deduce limits for the rotation and the mass of black holes. For this purpose we assume that a certain part of the anisotropies of the cosmic background radiation is due to absorption or superradiance of black holes (Teukolsky, 1973, Starobinskii and Churilov, 1973). The knowledge of these anisotropies yields bounds for rotation and mass of the black holes in the observable universe. 相似文献
13.
The recently discovered accelerated expansion of the universe is of current interest in theoretical research on the evolution
of the universe. The cause of this behavior is presumably the presence of dark energy, which has been estimated to form up
to 70% of the universe and generates a “repulsive force.” In this paper a cosmological model is constructed which takes the
dark energy into account in a Jordan-Brans-Dicke tensor-scalar model with a dominant, nonminimally coupled scalar field in
the presence of a cosmological scalar. The radiation dominant epoch is discussed.
__________
Translated from Astrofizika, Vol. 51, No. 1, pp. 151–159 (February 2008). 相似文献
14.
本文借助于观测到的大、小麦哲伦云的星际尘埃辐射，估计总星系内的“冷”星际尘埃热再辐射对宇宙微波背景辐射的影响．结果表明：总星系内的星际“冷”尘埃的热辐射所形成的背景辐射对微波背景辐射的扰动强烈地依赖于宇宙减速因子和“冷”尘埃量，在宇宙背景探测者（ＣＯＢＥ）的观测结果的限制下，无论宇宙减速因子取何种值，“冷”尘埃所占的比例都是非常少的，如果Ｏｓｔｒｉｋｅｒ所作的平均每个星系内由尘埃产生的蓝光光深τＢ＝０．５的假定是合理的，那么星际尘埃量随温度的分布是非常不均匀的。 相似文献
15.
Recently it has been argued that a possible source for the dark energy may arise due to the contribution to the vacuum energy
of the QCD ghost in a time-dependent background. In this paper we establish a connection between interacting ghost dark energy
and tachyon field. It is demonstrated that the evolution of the ghost dark energy dominated universe can be described completely
by a single tachyon scalar field. The potential and the dynamics of the tachyon field are reconstructed according to the evolutionary
behavior of ghost energy density. 相似文献
16.
《New Astronomy》2020
In this paper, we have presented an FLRW universe containing two-fluids (baryonic and dark energy), by assuming the deceleration parameter as a linear function of the Hubble function. This results in a time-dependent deceleration parameter (DP) having a transition from past decelerating to the present accelerating universe. In this model, dark energy (DE) interacts with dust to produce a new law for the density. As per our model, our universe is at present in a phantom phase after passing through a quintessence phase in the past. The physical importance of the two-fluid scenario is described in various aspects. The model is shown to satisfy current observational constraints such as recent Planck results. Various cosmological parameters relating to the history of the universe have been investigated. 相似文献
17.
K. H. Tsui 《Solar physics》1996,168(1):171-182
The generation of bright solar radio spikes by the beam-driven cyclotron resonance maser mechanism (the resonant interaction of an electron beam with a circularly polarized wave in a background plasma under the action of a guide magnetic field) is studied. Nonlinear effects such as radiation damping and gyrophase bunching on electron energy and momentum are responsible for the enhanced direct energy conversion between the beam and the coherent wave. Factors such as beam energy spread and pitch angle distribution are analyzed. The intense maser radiation is carried at the source by the circularly polarized wave propagating along the magnetic field. Due to the magnetic field curvature, the outgoing maser radiation converts into extraordinary and ordinary modes. The extraordinary mode suffers from plasma absorption at the second harmonic layer, whereas the ordinary mode is likely to get through. 相似文献
18.
Tarun Souradeep 《Journal of Astrophysics and Astronomy》1997,18(4):231-240
In this talk I outline some of the arguments in support of a cosmological and primordial origin of the observed microwave
background radiation (MBR) in the early hot phase of the universe. This interpretation of the MBR is at the heart of the hot
Big Bang model (HBBM) of the universe. The observed Planckian energy distribution of the microwave photons reflects the thermal
equilibrium that can be set up naturally within HBBM in the dense early universe. Alternate interpretations face the challenge
of extremely tight constraints on deviations from a Planckian distribution. Within HBBM, the formation of large scale structure
is linked to tiny anisotropies in the angular distribution of the MBR photons. Recent measurements of these anisotropies seem
to be broadly consistent with the predictions of the current scenarios of structure formation in the universe. Since these
predictions are based on HBBM, the concurrence of data with theory provides additional support in favour of viewing the MBR
as the relic of Big Bang. 相似文献
19.
Using Maxwell equations in a background metric discovered by Bonnor, which describes the gravitational field generated by an optimally charged dust ball, we calculate the external radiation field from an electric dipole source at the center the ball. Possible applications to stellar mode 1 s are discussed in the conclusions. 相似文献
20.
D. L. Khokhlov 《Astrophysics and Space Science》2011,335(2):577-580
The Einstein static model of the universe as a whole is considered. The Hubble law is explained by the Doppler effect due
to the downward inertial acceleration along a certain radius experienced by an observer in the center of the universe, with
the total acceleration over all radii being equal zero. Evolution of the universe is introduced through the wave function
of the universe dependent on time. This yields the energy density of the universe hence the temperature of the universe dependent
on time. On the contrary, the energy, forth and intensity of radiation are fixed with time that allows to develop the Newtonian
physics in the whole universe. The time-temperature relation of the universe in the model considered is the same as in the
radiation dominated universe in the Friedmann model that allows to explain primordial nucleosynthesis as it is in the standard
scenario. The modern parameters of the universe in the model considered are consistent with the observations. 相似文献