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1.
There are three independent techniques for determining the age of the Universe: via cosmochronology of long-lived radioactive nuclei, via stellar modelling and population synthesis of the oldest stellar populations, and, most recently, via the precision cosmology that has become feasible with the mapping of the acoustic peaks in the cosmic microwave background. We demonstrate that all three methods give completely consistent results, and enable us to set rigorous bounds on the maximum and minimum ages that are allowed for the Universe. We present new constraints on the age of the Universe by performing a multiband colour analysis of bright cluster ellipticals over a large redshift range     , which allows us to infer the ages of their stellar populations over a wide range of possible formation redshifts and metallicities. Applying a prior to Hubble's constant of     we find the age of the Universe to be     (1 σ ), in agreement with the estimates from Type Ia supernovae, as well as with the latest uranium decay estimates, which yield an age for the Milky Way of     . If we combine the results from cluster ellipticals with the analysis of the angular power spectrum of the cosmic microwave background and with the observations of Type Ia supernovae at high redshift, we find a similar age:     . Without the assumption of any priors, universes older than 18 Gyr are ruled out by the data at the 90 per cent confidence level.  相似文献   

2.
We discuss some of the major areas in astronomy and cosmology where plasma physics is important: (1) origin of stars; (2) distortions of the microwave background radiation; (3) expansion rate of the Early Universe; (4) the magnetic fields and relativistic electrons in jets; (5) the collimation of jets; (6) the origin of stellar winds; (7) the origin of filaments and clouds not gravitationally bound; and (8) the origin of cosmic rays.  相似文献   

3.
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   

4.
A number of large current experiments aim to detect the signatures of the cosmic reionization at redshifts z > 6. Their success depends crucially on understanding the character of the reionization process and its observable consequences and designing the best strategies to use. We use large-scale simulations of cosmic reionization to evaluate the reionization signatures at redshifted 21-cm and small-scale cosmic microwave background (CMB) anisotropies in the best current model for the background universe, with fundamental cosmological parameters given by Wilkinson Microwave Anisotropy Probe three-year results. We find that the optimal frequency range for observing the 'global step' of the 21-cm emission is 120–150 MHz, while statistical studies should aim at 140–160 MHz, observable by GMRT. Some strongly non-Gaussian brightness features should be detectable at frequencies up to ∼190 MHz. In terms of sensitivity-signal trade-off relatively low resolutions, corresponding to beams of at least a few arcminutes, are preferable. The CMB anisotropy signal from the kinetic Sunyaev–Zel'dovich effect from reionized patches peaks at tens of μK at arcminute scales and has an rms of ∼1 μK, and should be observable by the Atacama Cosmology Telescope and the South Pole Telescope. We discuss the various observational issues and the uncertainties involved, mostly related to the poorly known reionization parameters and, to a lesser extend, to the uncertainties in the background cosmology.  相似文献   

5.
We compare and combine likelihood functions of the cosmological parameters Ωm, h and σ 8, from peculiar velocities, cosmic microwave background (CMB) and type Ia supernovae. These three data sets directly probe the mass in the Universe, without the need to relate the galaxy distribution to the underlying mass via a 'biasing' relation. We include the recent results from the CMB experiments BOOMERANG and MAXIMA-1. Our analysis assumes a flat Λ cold dark matter (ΛCDM) cosmology with a scale-invariant adiabatic initial power spectrum and baryonic fraction as inferred from big-bang nucleosynthesis. We find that all three data sets agree well, overlapping significantly at the 2 σ level. This therefore justifies a joint analysis, in which we find a joint best-fitting point and 95 per cent confidence limits of     (0.17,0.39),     (0.64,0.86) and     (0.98,1.37). In terms of the natural parameter combinations for these data     (0.40,0.73),     (0.16,0.27). Also for the best-fitting point,     and the age of the Universe is 13.2 Gyr.  相似文献   

6.
The use of a cosmic potential in relativistic cosmology is criticized. It is pointed out that the energetic closure of the Universe follows from general relativity and from quantized superspace cosmology without the introduction of the cosmic potential.  相似文献   

7.
Non-linear evolution of cosmological energy density fluctuations triggers deviations from Gaussianity in the temperature distribution of the cosmic microwave background. A method to estimate these deviations is proposed. N -body simulations – in a Λ cold dark matter cosmology – are used to simulate the strongly non-linear evolution of cosmological structures. It is proved that these simulations can be combined with the potential approximation to calculate the statistical moments of the cosmic microwave background anisotropies produced by non-linear gravity. Some of these moments are computed and the resulting values are different from those corresponding to Gaussianity.  相似文献   

8.
During the nineteenth century, it was common for physicists to believe in the existence of a material vacuum composed of an incompressible fluid that fills the whole universe. This fluid was called the aether. Its original purpose was to provide an elastic tenuous medium for light propagation through space. Although it is well understood today that no such medium is needed for light propagation, the existence of a cosmic aether medium in space is still possible and its physical properties can be understood on models of cosmology that have nothing to do with Big-Bang cosmology. It is possible that electromagnetic radiation emitted by the cosmic aether medium has already been detected. The low-frequency electromagnetic radiation emitted by the aether is called the cosmic microwave background radiation. The present study outlines a model for an aether medium that explains the genesis of the microwave background radiation in a closed static (nonexpanding) universe. It is shown that the spectrum of the microwave background radiation is a perfect blackbody with a temperature T rad=2.77 K in harmony with the perfect cosmological principle. It is further shown that the aether medium is opaque at radio and microwave frequencies. This particular feature of the model does not contradict any observations regarding the existence of distant radio galaxies and quasars.  相似文献   

9.
The causal limit usually considered in cosmology is the particle horizon, delimiting the possibilities of causal connection in the expanding Universe. However, it is not a realistic indicator of the effective local limits of important interactions in space–time. We consider here the matter horizon for the Solar system, i.e. the comoving region which has significantly contributed matter to our local physical environment. This lies inside the effective domain of dependence , which (assuming the universe is dominated by dark matter along with baryonic matter and vacuum-energy-like dark energy) consists of those regions that have had a significant active physical influence on this environment through effects such as matter accretion and acoustic waves. It is not determined by the velocity of light c , but by the flow of matter perturbations along their world lines and associated gravitational effects. We emphasize how small a region the perturbations which became our Galaxy occupied, relative to the observable universe – even relative to the smallest scale perturbations detectable in the cosmic microwave background radiation. Finally, looking to the future of our local cosmic domain, we suggest simple dynamical criteria for determining the present domain of influence and the future matter horizon . The former is the radial distance at which our local region is just now separating from the cosmic expansion. The latter represents the limits of growth of the matter horizon in the far future.  相似文献   

10.
With the increasingly precise measurement of the cosmic microwave background (CMB), cosmology has entered an era where a model's predictions become testable to percent‐level accuracy. In particular, the CMB spectrum has so far provided impressive support for the scenario of inflation, first invented to solve outstanding problems of standard cosmology. While current data (COBE, WMAP etc.) have already constrained cosmological parameters like Ω0 to high precision, next generation instruments such as the PLANCK satellite should give access to specific characteristics of the inflationary mechanism itself. Another tantalizing idea has been discussed in this context: Given the enormous expansion of the Universe during the phase of inflation, could it be that even Planck scale physics has been stretched to observable distances and is therefore within grasp in the CMB observations? In this contribution, I discuss the possibility of carrying through the calculation of the perturbation spectrum from an ansatz for short distance physics right to its imprint in the CMB. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

11.
The temperature of the atomic matter in the Universe is held to that of the cosmic background radiation until decoupling at   z ∼ 100  . After this, it cools faster than the radiation [  ∝ (1 + z )2  rather than  (1 + z )  ] and would have fallen to about 20 mK today if astrophysical feedback processes had not heated up the interglactic medium. We show how the derivative of the Compton coupling equation helps numerically to follow the decoupling process.  相似文献   

12.
We use the billion-particle Hubble Volume simulations to make statistical predictions for the distribution of galaxy clusters that will be observed by the Planck Surveyor satellite through their effect on the cosmic microwave background – the Sunyaev–Zel'dovich (SZ) effect. We utilize the lightcone data sets for both critical density ( τ CDM) and flat low-density (ΛCDM) cosmologies: a 'full-sky' survey out to z ∼0.5 , two 'octant' data sets out to beyond z =1 , and a 100 square degree data set extending to z ∼4 . Making simple, but robust, assumptions regarding both the thermodynamic state of the gas and the detection of objects against an unresolved background, we present the expected number of SZ sources as a function of redshift and angular size, and also as a function of flux (for both the thermal and kinetic effects) for three of the relevant High Frequency Instrument frequency channels. We confirm the expectation that the Planck Surveyor will detect around 5×104 clusters, though the exact number is sensitive to the choice of several parameters including the baryon fraction, and also to the cluster density profile, so that either cosmology may predict more clusters. We also find that the majority of detected sources should be at z <1.5 , and we estimate that around 1 per cent of clusters will be spatially resolved by the Planck Surveyor , though this has a large uncertainty.  相似文献   

13.
A scheme is proposed for explaining the origin of the observed temperature of the cosmic microwave background (relict) radiation in which this radiation is treated as a product of the decay of primordial vector bosons in the framework of the Hoyle-Narlikar conformal cosmology.  相似文献   

14.
(a) Hubble's discovery of the expansion of the Universe makes it possible to choose unambiguously from the models described by Friedmann's equations of universe dynamics. (b) From the present temperature of the cosmic microwave background radiation, the specific entropy in the matter era and the model properties of the expansive nondecelerative universe, we can determine the present parameters of our Universe with deviations smaller than 2.2%.  相似文献   

15.
On the basis of the model properties of the expansive nondecelerative universe, present temperature of cosmic microwave background and specific entropy in the era of matter, the present parameters of our Universe may be exactly determined.  相似文献   

16.
I give a status report and outlook concerning the use of the cosmic microwave background anisotropies to constrain the inflationary cosmology, and stress its crucial role as an underlying paradigm for the estimation of cosmological parameters. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

17.
With WMAP putting the phenomenological standard model of cosmology on a strong footing, one can look forward to mining the cosmic microwave background (CMB) for fundamental physics with higher sensitivity and on smaller scales. Future CMB observations have the potential to measure absolute neutrino masses, test for cosmic acceleration independent of supernova Ia observations, probe for the presence of dark energy at z2, illuminate the end of the dark ages, measure the scale-dependence of the primordial power spectrum and detect gravitational waves generated by inflation.  相似文献   

18.
We explore the implications of a possible cosmic-ray (CR) background generated during the first supernova explosions that end the brief lives of massive Population III stars. We show that such a CR background could have significantly influenced the cooling and collapse of primordial gas clouds in minihaloes around redshifts of   z ∼ 15–20  , provided the CR flux was sufficient to yield an ionization rate greater than about 10−19 s−1 near the centre of the minihalo. The presence of CRs with energies  ≲107  eV would indirectly enhance the molecular cooling in these regions, and we estimate that the resulting lower temperatures in these minihaloes would yield a characteristic stellar mass as low as  ∼10 M⊙  . CRs have a less-pronounced effect on the cooling and collapse of primordial gas clouds inside more massive dark matter haloes with virial masses  ≳108 M⊙  at the later stages of cosmological structure formation around   z ∼ 10–15  . In these clouds, even without CR flux the molecular abundance is already sufficient to allow cooling to the floor set by the temperature of the cosmic microwave background.  相似文献   

19.
An alternative to dark energy as an explanation for the present phase of accelerated expansion of the Universe is that the Friedmann equation is modified, e.g. by extra dimensional gravity, on large scales. We explore a natural parametrization of a general modified Friedmann equation, and find that the present supernova Type Ia and cosmic microwave background data prefer a correction of the form 1/ H to the Friedmann equation over a cosmological constant.  相似文献   

20.
It is well known that the application of Newtonian dynamics to an expanding spherical region leads to the correct relativistic expression (the Friedmann equation) for the evolution of the cosmic scalefactor. Here, the cosmological implications of Milgrom's modified Newtonian dynamics (MOND) are considered by means of a similar procedure. Earlier work by Felten demonstrated that in a region dominated by modified dynamics the expansion cannot be uniform (separations cannot be expressed in terms of a scalefactor) and that any such region will eventually recollapse regardless of the initial expansion velocity and mean density. Here I show that, because of the acceleration threshold for the MOND phenomenology, a region dominated by MOND will have a finite size which, in the earlier Universe ( z >3), is smaller than the horizon scale. Therefore, uniform expansion and homogeneity on the horizon scale are consistent with MOND-dominated non-uniform expansion and the development of inhomogeneities on smaller scales. In the radiation-dominated era, the amplitude of MOND-induced inhomogeneities is much smaller than that implied by observations of the cosmic background radiation, and the thermal and dynamical history of the Universe is identical to that of the standard big bang model. In particular, the standard results for primordial nucleosynthesis are retained. When matter first dominates the energy density of the Universe, the cosmology diverges from that of the standard model. Objects of galaxy mass are the first virialized objects to form (by z =10), and larger structure develops rapidly. At present, the Universe would be inhomogeneous out to a substantial fraction of the Hubble radius.  相似文献   

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