共查询到20条相似文献，搜索用时 531 毫秒
1.
V. V. Burdyuzha 《Astronomy Reports》2012,56(6):403-409
The evolution of the vacuum component of the Universe is studied in both the quantum and classical regimes. Our Universe has emerged as a result of a tunneling process, beginning with an oscillating mode and passing on to a Friedmann mode, and it very probably had a high symmetry for the Planck parameters. In the first fractions of a second (the quantum regime), as it cooled, the vacuum component of the Universe lost its high degree of symmetry due to phase transitions; i.e., its positive energy density was subject to negative contributions from quantum field condensates (by 78 orders of magnitude). After the last (quark-hadron) phase transition, the vacuum energy ??froze.?? At this time (10?6 s), the vacuum energy density can be calculated using the formula of Zel??dovich and substituting the mean values of the pseudo-Goldstone boson (??-mesons) masses characterizing the chromodynamic vacuum. Chiral symmetrywas lost at that time. The dynamics of the equilibrium vacuum after its ??hardening?? is considered using the holographic principle. During the next 4 × 1017 s (the classical regime), the vacuum component of the Universe was reduced by 45 orders of magnitude due to the creation of new quantum states during its expansion. It is possible to solve the cosmological-constant problem using the holographic principle, since the 123 problematic orders of magnitude disappear in usual physical processes. The vacuum energy density is also calculated in the classical regime to a redshift of 1011 using a ??cosmological calculator.?? 相似文献
2.
L. M. Chechin 《Astronomy Reports》2016,60(6):535-541
A step-by-step foundation for the differential character of the Universe’s rotation is presented. First, invoking the concept of spacetime foam with spin, it is reasonable to assume that the very early Universe can be described by the Dirac equation. Second, it is shown using the Ehrenfest theorem that, from a classical point of view, the early Universe can be described by the Papapetrou equations. Third, it is stressed that our Universe can perform only rotational motion. It is shown based on the spin part of the Papapetrou equations that the Universe’s rotation depends appreciably on the physical properties of a specific cosmological epoch. The rotational angular velocity is calculated for three basic cosmological epochs: the matter-dominated epoch, the transition period (from domination of matter to domination of vacuum), and the vacuum-dominated epoch. 相似文献
3.
D. D. Sokoloff 《Astronomy Reports》2003,47(12):975-978
A cosmological scenario in which the topology of the Universe is treated like a dynamical time-dependent variable is put forward. The Universe could be small in an initial quantum stage of evolution and then gradually increase its dimensions so that the present-day nontrivial topology is manifest only far beyond the cosmological horizon. 相似文献
4.
The polarization-correction energy-momentum tensor for a semi-classical gravitational theory is derived. This tensor accounts for the creation of particles from a vacuum at a finite temperature. The theory contains an asymptotic cosmological Friedmann solution. The solution obtained turns out to be dynamically stable, so that it can form the observed properties of the Universe. New cosmological solutions describing the early stages of cosmological evolution of a homogeneous isotropic Universe are obtained. One of these corresponds to the simultaneous creation of matter and geometry from the vacuum of a flat, empty space-time without structure. Another solution corresponds to a high-temperature inflation regime. A cosmological scenario for the creation of the observed Universe from “nothing” that includes the properties of all the solutions obtained is put forward. 相似文献
5.
We consider models of a wormhole (i) maintained by an electromagnetic field, taking into account quantum vacuum corrections to the equation of state, (ii) maintained by a combination of the magnetic field and phantom energy, with a spherically symmetrical equation of state, and (iii) with a magnetic field and phantom matter with an anisotropic equation of state. It is shown that the quantum corrections and the density and exoticity of phantom energy or matter can be as small as is desired. For an external observer, the entrance to the tunnel appears to be a magnetic monopole of macroscopic size. The accretion of ordinary matter onto the entrance to the tunnel may result in the formation of a black hole with a radial magnetic field. We consider the possibility that some active galactic nuclei and Galactic objects may be current or former entrances to magnetic wormholes. We consider the possible existence of a broad mass spectrum for wormholes, from several billion solar masses to masses of the order of 2 kg. The Hawking effect (evaporation) does not operate in such objects due to the absence of a horizon, making it possible for them to be retained over cosmological time intervals, even if their masses are smaller than 1015 g. We also discuss a model for a binary system formed by the entrances of tunnels with magnetic fields, which could be sources of nonthermal radiation and γ-ray bursts. 相似文献
6.
Cosmological large numbers are studied using dimensional analysis. Expressions linking cosmological parameters with fundamental constants of the microworld are proposed. The Zel’dovich formula for the cosmological constant is generalized, and a series of characteristic masses of the Universe is derived. 相似文献
7.
The solution of the Friedmann cosmological equations for the scale factor in a model of the Universe containing matter having the equation of state of dust and dark energy is considered. The equation-of-state parameter of the dark energy is taken to be an arbitrary constant w = ?1.006 ± 0.045, whose value is constrained by the current observational limits. An exact solution for the scale factor as a function of physical time and conformal time is obtained. Approximate solutions have been found for the entire admissible conformal time interval with an accuracy better than 1%, which exceeds the accuracy of the determined global parameters of our Universe. This is the first time an exact solution for the scale factor describing the evolution of the Universe in a unified way, beginning with the matter-dominated epoch and ending with the infinitely remote future, has been obtained. 相似文献
8.
We briefly review the history of the cosmological constant. Recently discovered accelerated expansion epoch of the universe placed the problem of the cosmological constant at a forefront of interest of astronomers and physicists. Short account of recent developments is given. 相似文献
9.
The presence of ultrahigh-energy (UHE) cosmic rays results in an increase in the degree of ionization in the post-recombination Universe, which stimulates the efficiency of the production of H2 molecules and the formation of the first stellar objects. As a result, the onset of the formation of the first stars is shifted to higher redshifts, and the masses of the first stellar systems decrease. As a consequence, a sufficient increase in the ionizing radiation providing the reionization of the Universe can occur. We discuss the possible observational manifestations of these effects and their dependence on the parameters of UHE cosmic rays. 相似文献
10.
The conditions for the fragmentation of the baryonic component during mergers of dark matter halos in the early Universe are studied. We assume that the baryonic component undergoes a shock compression. The characteristic masses of protostellar molecular clouds and the minimum masses of protostars originating in these clouds decrease with increasing halo mass. This may indicate that the initial stellar mass function in more massive galaxies was shifted towards lower masses during the initial stages of their formation. This would result in an increase in the number of stars per unit mass of the halo, i.e., in an increase in the efficiency of star formation. 相似文献
11.
O. V. Verkhodanov A. I. Kopylov Yu. N. Pariiskii N. S. Soboleva A. V. Temirova O. P. Zhelenkova 《Astronomy Reports》2002,46(7):531-542
BV RI data are presented for the majority of steep-spectrum objects in the RC catalog with m R <23.5m. Previously developed programs are applied to these data to estimate the redshifts and ages of the stellar systems of the host galaxies. Applying this program to the color data (BV RI JHK) for distant radio galaxies with spectroscopic redshifts indicates that this approach provides accurate estimates of the redshifts of such radio galaxies, close to those obtained using field galaxies (～20%). The age estimates are much less trustworthy, but a lower limit to the ages of objects that are not very distant (z<1.5) can be determined with certainty. We have identi fied several galaxies whose formal ages exceed the age of the Universe at the corresponding z in simple Cold Dark Matter models for the Universe. The possibility of using such objects to elucidate the role of “dark energy” is discussed. This paradox disappears in models with cosmological constants (Λ terms) equal to 0.6–0.8. 相似文献
12.
It is known that ΛCDM cosmological models predict too many dark halos compared to the observed numbers. This excess is derived from the virialized mass in the Local Supercluster and its vicinity. Taking into account cosmological velocity fluctuations during the formation of the dark halo population makes it possible to eliminate this remaining contradiction in the ΛCDM model. Based on Press-Schechter formalism, a model describing the formation of the dark halo population is developed, taking into account kinematic effects in the dark matter. A quantitative explanation of the virialized-mass deficit in the local Universe is obtained in this model. 相似文献
13.
The “Scenario Machine” (a computer code designed for studies of the evolution of close binaries) was used to carry out a population synthesis for a wide range of merging astrophysical objects: main-sequence stars with main-sequence stars; white dwarfs with white dwarfs, neutron stars, and black holes; neutron stars with neutron stars and black holes; and black holes with black holes. We calculate the rates of such events, and plot the mass distributions for merging white dwarfs and main-sequence stars. It is shown that Type Ia supernovae can be used as standard candles only after approximately one billion years of evolution of galaxies. In the course of this evolution, the average energy of Type Ia supernovae should decrease by roughly 10%; the maximum and minimum energies of Type Ia supernovae may differ by no less than by a factor of 1.5. This circumstance must be taken into account at estimating the parameters of the Universe expansion acceleration. According to theoretical estimates, the most massive—as a rule, magnetic—white dwarfs probably originate from mergers of white dwarfs of lower mass. At least some magnetic Ap and Bp stars may form in mergers of low-mass main-sequence stars (M ? 1.5 M ⊙) with convective envelopes. 相似文献
14.
The bolometric flux deficits of the photospheres of spotted stars are derived for the first time in the framework of zonal spottedness models for red dwarfs computed at the Crimean Astrophysical Observatory. The resulting flux deficits are compared to the estimated radiative losses from the chromospheres and coronas measured during quasi-simultaneous observations. A linear correlation is found between the logarithms of these quantities, with the Sun fitting these relations. Radiative losses from the outer stellar atmospheres in quiescence and during individual sporadic flares are significantly lower than the bolometric deficits of the spotted photospheres of active stars. This suggests that the flux deficit due to spots leads to global reconstruction of the atmospheres of red dwarfs, analogous to the local atmospheric reconstruction that occurs during solar and stellar flares. This process may be realized via the superposition of a large number of weak impulsive flares and other dynamic events, which develop on these stars and heat their coronas (i.e., in this view, microflaring is favored as the principal coronal heating mechanism for these stars). A brief analysis of the long-term variations in the chromospheric and photospheric radiation of F-K stars from the HK project and of the Sun suggests that such dynamical reconstruction of the outer atmosphere by energy associated with the flux deficit of the spotted photosphere occurs at times of increased surface activity in all F-M stars. 相似文献
15.
G. A. Shul’man 《Astronomy Reports》2011,55(8):718-723
The quantum motion of non-relativistic and relativistic electrons in the presence of constant magnetic fields at the surfaces of magnetic stars, magnetic white dwarfs, and pulsars is considered. The quantizing magnetic-field strengths for charged particles with specified energies are determined. The quantum motion of these particles in a plane perpendicular to the magnetic field is accompanied by spontaneous radiation due to electron transitions from higher to lower discrete energy levels, right down to the ground state. In the non-relativistic case, this emission is monochromatic. In the non-relativistic case, various frequencies are emitted, but lie within an order of magnitude of each other. The electron kinetic energy along the magnetic field varies from zero to a maximum value, due to the one-dimensional character of the motion along the field, between each pair of potential barriers corresponding to the discrete energy levels. The results may be relevant to describing gamma-ray flares of pulsars. 相似文献
16.
The standard equations of general relativity admit extension so that they can be supplemented, not only with Einsteinian cosmological
repulsive forces described by the Λ term, but also with other forces. Accordingly, we suggest a model of a uniformly expanding
Universe (an S model). In this model, the cosmological forces of attraction and repulsion precisely balance each other. This
S model is a good approximation for describing the Universe’s evolution over a wide range of redshifts (up to z ∼ 1000). The S model can explain in a simple way observational data on the age of the Universe, the apparent magnitude-redshift
relation for Type Ia supernovae, and the angular separation between the centers of neighboring bright spots against the uniform
background of the cosmic microwave background radiation. 相似文献
17.
R. Vargas E.A. Yépez J.L. Andrade G. Ángeles T. Arredondo A.E. Castellanos J. Delgado-Balbuena J. Garatuza-Payán E. González Del Castillo W. Oechel J.C. Rodríguez A. Sánchez-Azofeifa E. Velasco E.R. Vivoni C. Watts 《Atmósfera》2013,26(3):325-336
Understanding ecosystem processes from a functional point of view is essential to study relationships among climate variability, biogeochemical cycles, and surface-atmosphere interactions. Increasingly during the last decades, the eddy covariance (EC) method has been applied in terrestrial, marine and urban ecosystems to quantify fluxes of greenhouse gases (e.g., CO2, H2O) and energy (e.g., sensible and latent heat). Networks of EC systems have been established in different regions and have provided scientific information that has been used for designing environmental and adaptation policies. In this context, this article outlines the conceptual and technical framework for the establishment of an EC regional network (i.e., MexFlux) to measure the surface-atmosphere exchange of heat and greenhouse gases in Mexico. The goal of the network is to improve our understanding of how climate variability and environmental change influence the dynamics of Mexican ecosystems. First, we discuss the relevance of CO2 and water vapor exchange between terrestrial ecosystems and the atmosphere. Second, we briefly describe the EC basis and present examples of measurements in terrestrial and urban ecosystems of Mexico. Finally, we describe the conceptual and operational goals at short-, medium-, and long-term scales for continuity of the MexFlux network. 相似文献
18.
In this study, we discuss the challenges radio astronomers face while observing radio continuum sources. We consider issues related to rms noise, confusion, position accuracy, shot noise and how these issues affect observation results, data analysis and the science goals we are trying to achieve. We mainly focus on the Evolutionary Map of the Universe (EMU-ASKAP) sky survey, EMU Early science survey and Westerbork Observations of the Deep APERTIF Northern sky (WODAN). The study will also be useful for future surveys like with possible continuum surveys through MeerKAT (e.g., MIGHTEE) and SKA-1. The late time Integrated Sachs-Wolfe (ISW) effect detection is one of the major areas of research related to dark energy cosmology. We will particularly discuss how technical, data analysis and mapping issues, affect galaxy over/under density dependent science goals like the detection of the late time Integrated Sachs-Wolfe (ISW) effect through wide-field radio continuum surveys.
相似文献19.
We present a new normalization for the linear density-perturbation spectrum in a multi-parameter model of the Universe. Using the differential mass function for the nearly galaxy clusters obtained from optical data, we have constructed a functional relation between the dispersion of the density contrast σ 8 on the scale 8h ?1 Mpc and the cosmological parameters Ω m , ΩΛ, h, n, f v for each of three theoretical approximations of the mass function: Press-Schechter, Sheth-Tormen and Jenkins. An extended class of models of the Universe with general spatial curvature include four parameters for the matter components: baryons (Ω b ), “cold” dark matter (Ω c ), “hot” dark matter (Ω v ), and the vacuum energy (ΩΛ). It is shown that the most accurate normalization of the power spectrum is achieved with the Sheth-Tormen approximation. 相似文献
20.
M. M. Katsova L. L. Kitchatinov M. A. Livshits D. L. Moss D. D. Sokoloff I. G. Usoskin 《Astronomy Reports》2018,62(1):72-80
Recent data from the Kepler mission has revealed the occurrence of superflares in Sun-like stars which exceed by far any observed solar flares in released energy. Radionuclide data do not provide evidence for occurrence of superflares on the Sun over the past eleven millennia. Stellar data for a subgroup of superflaring Kepler stars are analysed in an attempt to find possible progenitors of their abnormal magnetic activity. A natural idea is that the dynamo mechanism in superflaring stars differs in some respect from that in the Sun. We search for a difference in the dynamo-related parameters between superflaring stars and the Sun to suggest a dynamo mechanism as close as possible to the conventional solar/stellar dynamo but capable of providing much higher magnetic energy. Dynamo based on joint action of differential rotation and mirror asymmetric motions can in principle result in excitation of two types of magnetic fields. First of all, it is well-known in solar physics dynamo waves. The point is that another magnetic configuration with initial growth and further stabilisation can also be excited. For comparable conditions, magnetic field of second configuration is much stronger than that of the first one just because dynamo does not spend its energy for periodic magnetic field inversions but uses it for magnetic field growth. We analysed available data from the Kepler mission concerning the superflaring stars in order to find tracers of anomalous magnetic activity. As suggested in a recent paper [1], we find that anti-solar differential rotation or anti-solar sign of the mirror-asymmetry of stellar convection can provide the desired strong magnetic field in dynamo models. We confirm this concept by numerical models of stellar dynamos with corresponding governing parameters. We conclude that the proposed mechanism can plausibly explain the superflaring events at least for some cool stars, including binaries, subgiants and, possibly, low-mass stars and young rapid rotators. 相似文献