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1.
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
2.
A new dark energy model in anisotropic Bianchi type-III space-time with variable equation of state (EoS) parameter has been
investigated in the present paper. To get the deterministic model, we consider that the expansion θ in the model is proportional to the eigen value s2 2\sigma^{2}_{~2} of the shear tensor sj i\sigma^{j}_{~i}. The EoS parameter ω is found to be time dependent and its existing range for this model is in good agreement with the recent observations of
SNe Ia data (Knop et al. in Astrophys. J. 598:102, 2003) and SNe Ia data with CMBR anisotropy and galaxy clustering statistics (Tegmark et al. in Astrophys. J. 606:702, 2004). It has been suggested that the dark energy that explains the observed accelerating expansion of the universe may arise
due to the contribution to the vacuum energy of the EoS in a time dependent background. Some physical aspects of dark energy
model are also discussed. 相似文献
3.
《New Astronomy》2017
The observational cosmology with distant Type Ia supernovae (SNe) as standard candles claims that the Universe is in accelerated expansion, caused by a large fraction of dark energy. In this paper we investigate the SN Ia environment, studying the impact of the nature of their host galaxies on the Hubble diagram fitting. The supernovae (192 SNe) used in the analysis were extracted from Joint-Light-curves-Analysis (JLA) compilation of high-redshift and nearby supernovae which is the best one to date. The analysis is based on the empirical fact that SN Ia luminosities depend on their light curve shapes and colors. We confirm that the stretch parameter of Type Ia supernovae is correlated with the host galaxy type. The supernovae with lower stretch are hosted mainly in elliptical and lenticular galaxies. No significant correlation between SN Ia colour and host morphology was found. We also examine how the luminosities of SNe Ia change depending on host galaxy morphology after stretch and colour corrections. Our results show that in old stellar populations and low dust environments, the supernovae are slightly fainter. SNe Ia in elliptical and lenticular galaxies have a higher α (slope in luminosity-stretch) and β (slope in luminosity-colour) parameter than in spirals. However, the observed shift is at the 1-σ uncertainty level and, therefore, can not be considered as significant. We confirm that the supernova properties depend on their environment and that the incorporation of a host galaxy term into the Hubble diagram fit is expected to be crucial for future cosmological analyses. 相似文献
4.
A new class of exact solutions of Einstein’s field equations with a bulk viscous fluid for an LRS Bianchi type-Ia obtained
by using a time dependent deceleration parameter and cosmological term Λ. The coefficient of bulk viscosity is assumed to
be a power function of mass density (ξ=ξ
0
ρ
n
). We have obtained a general solution of the field equations from which six models of the universe are derived: exponential,
polynomial and sinusoidal form respectively. The behaviour of these models of the universe are also discussed in the frame
of reference of recent supernovae Ia observations.
相似文献
5.
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
6.
The universe with adiabatic matter creation is considered. It is thought that the negative pressure caused by matter creation
can play the role of a dark energy component, and drive the accelerating expansion of the universe. Using the Type Ia supernovae
(SNe Ia) data, the observational Hubble parameter data, the Cosmic Microwave Background (CMB) data and the Baryonic Acoustic
Oscillation (BAO) data, we make constraints on the cosmological parameters, assuming a spatially flat universe. Our results
show that the model with matter creation is consistent with the SNe Ia data, while the joint constraints of all these observational
data disfavor this model. If the cosmological constant is taken into account, a traditional model without matter creation
is favored by the joint observations. 相似文献
7.
Exact solution of Einstein’s field equations is obtained for massive string cosmological model of Bianchi III space-time using
the technique given by Letelier (Phys. Rev. D 20:2414, 1983) in presence of perfect fluid and decaying vacuum energy density Λ. To get the deterministic solution of the field equations
the expansion θ in the model is considered as proportional to the eigen value s2 2\sigma^{2}_{~2} of the shear tensor sj i\sigma^{j}_{~i} and also the fluid obeys the barotropic equation of state. The vacuum energy density Λ is found to be positive and a decreasing
function of time which is supported by the results from recent supernovae Ia observations. It is also observed that in early
stage of the evolution of the universe string dominates over the particle whereas the universe is dominated by massive string
at the late time. Some physical and geometric properties of the model are also discussed. 相似文献
8.
A five dimensional Kaluza-Klein space-time is considered in the presence of prefect fluid source in the general scalar-tensor
theory of gravitation proposed by Nordtvedt (Astrophys. J. 161:1069, 1970) with the help of special law of variation for Hubble’s parameter given by Bermann (Nuovo Cimento 74B:182, 1983). A cosmological model with a negative constant deceleration parameter is obtained in this theory. Some physical properties
of the model are also discussed. 相似文献
9.
P. Ruiz-Lapuente 《Astrophysics and Space Science》2004,290(1-2):43-59
This review gives an update of the cosmological use of SNe Ia and the progress made in testing their properties from the local universe to high-z. The cosmological road from high-z supernovae down to Galactic SNe Ia is followed in search of the answer to standing questions on their nature and their validity as cosmological indicators. 相似文献
10.
Brad E. Tucker 《Astrophysics and Space Science》2011,335(1):223-230
Type Ia Supernova (SN Ia) are a powerful, albeit not completely understood, tool for cosmology. Gaps in our understanding
of their progenitors and detailed physics can lead to systematic errors in the cosmological distances they measure. We use
UV data in two context to help further our understanding of SN Ia progenitors and physics. We analyze a set of nearly 700
light curves, and find no signature of the shock heating of a red giant companion, predicted by Kasen (Astrophys. J. 708:1025,
2010), casting doubt as to frequency of this SN Ia channel. We also use UV imaging of high redshift host galaxies of SN Ia to
better understand the environments which SN Ia occur. We show that some high-z elliptical galaxies have current star formation, hindering efforts to use them as low-extinction environments. We show cosmological
scatter of SN distances at large effective radii in their hosts is significantly reduced, and argue this is due to the smaller
amounts of dust affecting the SN Ia. Finally, we find a two component dependence of SN distance measurements as a function
of their host galaxy’s FUV-V color. This indicates that both the age and metallicity/mass of the host galaxy maybe important
ingredients in measuring SN Ia distances. 相似文献
11.
The present study deals with a spatially homogeneous and anisotropic Bianchi-I cosmological models representing massive strings.
The energy-momentum tensor, as formulated by Letelier (1983), has been used to construct massive string cosmological models for which we assume the expansion scalar in the models is
proportional to one of the components of shear tensor. The Einstein’s field equations have been solved by applying a variation
law for generalized Hubble’s parameter in Bianchi-I space-time. We have analysed a comparative study of accelerating and decelerating
models in the presence of string scenario. The study reveals that massive strings dominate in the decelerating universe whereas
strings dominate in the accelerating universe. The strings eventually disappear from the universe for sufficiently large times,
which is in agreement with current astronomical observations. 相似文献
12.
Hasmukh K. Tank 《Astrophysics and Space Science》2011,336(2):341-343
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
13.
A special law of variation for Hubble’s parameter is presented in a spatially homogeneous and anisotropic Bianchi type-I space-time
that yields a constant value of deceleration parameter. Using the law of variation for Hubble’s parameter, exact solutions
of Einstein’s field equations are obtained for Bianchi-I space-time filled with perfect fluid in two different cases where
the universe exhibits power-law and exponential expansion. It is found that the solutions are consistent with the recent observations
of type Ia supernovae. A detailed study of physical and kinematical properties of the models is carried out. 相似文献
14.
A self-consistent method has been evolved to infer physical parameters like density, radiation field and abundances using
line and continuum radiations as diagnostics. For that purpose, we first calculate the temperatures of graphite and silicate
grains using the model of Li and Draine (Astrophys. J. 554:778, 2001) by solving self-consistently the energy balance for G
0 (1–104) times the radiation field following Weingartner and Draine (Astrophys. J. Suppl. Ser. 134:263, 2001). Consequently, infrared emission fluxes are also obtained. To keep it simple, this is presented in the empirical form of
parameters T
D
and wavelength. The same model of the grain is adopted for photoelectric heating of gas using the formalism of Weingartner
and Draine (Astrophys. J. Suppl. Ser. 134:263, 2001) (hereafter referred to as WD) and Bakes and Tielens (Astrophys. J. 427:822, 1994) (hereafter referred to as BT) for radiation field cited above in the range (6<hν≤13.6 eV). Temperature and abundances are determined using our own code for PDR very similar to cloudy code. All the possible
sources of heating and cooling are considered for setting up the thermal balance. For the gas phase abundances that vary with
depth in the cloud due to dust, self- and mutual shielding, chemical balance is solved. Most of the photoionization, photodissociation
or chemical reaction rates are taken from UMIST database. We present an analysis of the cooling lines of singly ionized carbon
[CII] at 158 μm and neutral oxygen [OI], at 63 μm and far infrared (FIR) continuum for a variety of star forming galaxies.
Method of analysis of observational data is different from that of Malhotra et al. (Astrophys. J. 561:766, 2001). The radiation field G
0, density N
h
and abundance of carbon are obtained through best fit of observed and calculated intensities for lines and continuum radiations. 相似文献
15.
Marcelo Samuel Berman 《Astrophysics and Space Science》2012,337(1):477-481
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
16.
The single-degenerate (SD) channel for the progenitors of type Ia supernovae (SNe Ia) is one of the most popular channels, in which a carbon–oxygen white dwarf (CO WD) accretes hydrogen-rich material from its companion, increases its mass to the Chandrasekhar mass limit, and then explodes as a SN Ia. We show the initial and final parameter space for SNe Ia in a ( $\log P^{\mathrm{i}},M_{2}^{\mathrm{i}}$ ) plane and find that the positions of some famous recurrent novae, as well as a supersoft X-ray source (SSS), RX J0513.9-6951, are well explained by our model. The model can also explain the space velocity and mass of Tycho G, which is now suggested to be the companion star of Tycho’s supernova. Our study indicates that the SSS, V Sge, might be the potential progenitor of supernovae like SN 2002ic if the delayed dynamical-instability model due to Han and Podsiadlowski (Mon. Not. R. Astron. Soc. 368:1095, 2006) is appropriate. Following the work of Meng et al. (Mon. Not. R. Astron. Soc. 395:2103, 2009a), we found that the SD model (WD+MS) with an optically thick wind can explain the birth rate of supernovae like SN 2006X and reproduce the distribution of the color excess of SNe Ia. The model also predicts that at least 75% of all SNe Ia may show a polarization signal in their spectra. 相似文献
17.
The Theory of Alfven drag (Drell et al. in J Geophys Res 70: 3131–3145 1965; Anselmo and Farinella in Icarus, 58, 182–185 1983) is applied here to show that the existence of a possible solar ring structure at a radial distance of 0.02 AU (~4R
⊙
, R
⊙
= radius of the sun) predicted by earlier authors (Brecher et al. in Nature 282, 50–52 1979; Rawal in Bull. Astr. Soc. India 6, 92–95 1978, Moon Planets 24, 407–414 1981, Moon Planets 31, 175–182 1984, J Astrophys Astr 10, 257–259 1989) may not survive Alfven drag produced during even moderate solar magnetic storms which take place from time to time through
the age of the sun, but a possible solar ring structure at a radial distance of 0.13 AU (~27R
⊙
) (Brecher et al. in Nature 282, 50–52 1979; Rawal in Bull. Astr. Soc. India 6, 92–95 1978, Moon Planets 24, 407–414 1981, Moon Planets 31, 175–182 1984, J Astrophys Astr 10, 257–259 1989) may survive intense Alfven drag produced during even strong magnetic storms of magnetic field value up to 1,000 G. 相似文献
18.
LRS Bianchi type-I dark energy model with variable equation of state (EoS) parameter is presented in the scalar-tensor theory
of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986). To get a determinate solution of the field equations we take the help of special law of variation for Hubble’s parameter
presented by Bermann (Nuovo Cimento B 74:182, 1983) which yields a cosmological model with negative constant deceleration parameter. Some physical and kinematical properties
of the model are also discussed. 相似文献
19.
We present the cosmological parameters constraints obtained from the combination of galaxy cluster mass function measurements (Vikhlinin et al. 2009a, 2009b) with new cosmological data obtained during last three years: updated measurements of cosmic microwave background anisotropy with Wilkinson Microwave Anisotropy Probe (WMAP) observatory, and at smaller angular scales with South Pole Telescope (SPT), new Hubble constant measurements, baryon acoustic oscillations and supernovae Type Ia observations. New constraints on total neutrino mass ??m ?? and effective number of neutrino species are obtained. In models with free number of massive neutrinos the constraints on these parameters are notably less strong, and all considered cosmological data are consistent with non-zero total neutrino mass ??m ?? ?? 0.4 eV and larger than standard effective number of neutrino species, N eff ?? 4. These constraints are compared to the results of neutrino oscillations searches at short baselines. The updated dark energy equation of state parameter constraints are presented. We show that taking in account systematic uncertanties, current cluster mass funstion data provide similarly powerful constraints on dark energy equation of state, as compared to the constraints from supernovae Type Ia observations. 相似文献
20.
Marcelo Samuel Berman 《Astrophysics and Space Science》2008,314(1-3):79-82
A combined BCDE (Brans-Dicke and Einstein-Cartan) theory with lambda-term is developed through Raychaudhuri’s equation, for
inflationary scenario. It involves a variable cosmological constant, which decreases with time, jointly with energy density,
cosmic pressure, shear, vorticity, and Hubble’s parameter, while the scale factor, total spin and scalar field increase exponentially.
The post-inflationary fluid resembles a perfect one, though total spin grows, but the angular speed does not (Astrophys. Space
Sci. 312: 275, 2007d).
相似文献