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Том 60, № 6 (2016)

Article

Rotation of the Universe at different cosmological epochs

Chechin L.

Аннотация

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.

Astronomy Reports. 2016;60(6):535-541
pages 535-541 views

Detail studies of the physical properties in the outer regions of galaxy clusters using Suzaku observations

Babyk Y.

Аннотация

A detailed physical analysis of five nearby galaxy clusters using Suzaku observationsis presented. The low and stable level of the instrumental background at large radii facilitate the determination of the main physical characteristics in clusters at the virial radius. The temperatures, metal abundances, and entropy profiles have been constructed out to the outskirts of the clusters. The temperature profiles all display the same shape, with a negative gradient towards to the center and a flat outer plateau. The strong temperature gradients in the central parts of the clusters are usually associated with strong peaks of the surface brightness profiles. The temperature systematically decrease outward from the central regions, by a factor of three at and slightly beyond the cluster outskirts. The temperature profiles are compared with profiles predicted by N-body and hydrodynamical simulations obtained using several numerical algorithms. The slopes in the observed and simulated temperature profiles are consistent with each other in the cluster outskirts. The central regions of the clusters are characterized by low entropy and high metallicity. The possible influence of cool cores on the cluster outskirts is also discussed. The total mass profiles were determined using the observed gas-density and temperature profiles, assuming hydrostatic equilibriumand spherical symmetry. The gas-density profiles were fitted using an improved three-dimensional model to fit the inner and outer regions of the cluster independently. The total mass profiles were described using an NFW model out to R200. The measurements show clear evidence for universality of the total mass distribution. The scaled mass profiles in units of R200 and M200 display a dispersion of ~15% at 0.1R200. The fraction of gas out to R200 was also found.

Astronomy Reports. 2016;60(6):542-562
pages 542-562 views

Large-scale fluctuations in the number density of galaxies in independent surveys of deep fields

Shirokov S., Lovyagin N., Baryshev Y., Gorokhov V.

Аннотация

New arguments supporting the reality of large-scale fluctuations in the density of the visible matter in deep galaxy surveys are presented. A statistical analysis of the radial distributions of galaxies in the COSMOS and HDF-N deep fields is presented. Independent spectral and photometric surveys exist for each field, carried out in different wavelength ranges and using different observing methods. Catalogs of photometric redshifts in the optical (COSMOS-Zphot) and infrared (UltraVISTA) were used for the COSMOS field in the redshift interval 0.1 < z < 3.5, as well as the zCOSMOS (10kZ) spectroscopic survey and the XMM-COSMOS and ALHAMBRA-F4 photometric redshift surveys. The HDFN-Zphot and ALHAMBRA-F5 catalogs of photometric redshifts were used for the HDF-N field. The Pearson correlation coefficient for the fluctuations in the numbers of galaxies obtained for independent surveys of the same deep field reaches R = 0.70 ± 0.16. The presence of this positive correlation supports the reality of fluctuations in the density of visible matter with sizes of up to 1000 Mpc and amplitudes of up to 20% at redshifts z ~ 2. The absence of correlations between the fluctuations in different fields (the correlation coefficient between COSMOS and HDF-N is R = −0.20 ± 0.31) testifies to the independence of structures visible in different directions on the celestial sphere. This also indicates an absence of any influence from universal systematic errors (such as “spectral voids”), which could imitate the detection of correlated structures.

Astronomy Reports. 2016;60(6):563-578
pages 563-578 views

MHD accretion of a perfect fluid with an ultrahard equation of state onto a moving Schwarzschild black hole

Chernov S.

Аннотация

The full version of the magnetohydrodynamical (MHD) theory of accretion of a perfect fluid with an ultrahard equation of state, p = μ ~ ρ2 (where p is the pressure, μ the total energy density, and ρ the fluid density), onto a moving Schwarzschild black hole is considered. Exact and approximate analytical solutions have been found. It is shown that smooth continuous solutions exist only in the case when a single critical sound surface is formed.

Astronomy Reports. 2016;60(6):579-585
pages 579-585 views

Influence of small-scale magnetic field on the reverse positron current in the inner gaps of radio pulsars

Barsukov D., Goglichidze O., Tsygan A.

Аннотация

The reverse positron current flowing through the inner gap of an old radio pulsar in the presence of a small-scale magnetic field is found. Computations for the case of both strong and weak screening of the longitudinal electric field by the electron–positron plasma are presented.

Astronomy Reports. 2016;60(6):586-597
pages 586-597 views

Estimation of the radius of a star based on its effective temperature and surface gravity

Sichevskij S.

Аннотация

Amethod for determining the radius of a star using its effective temperature and surface gravity is proposed. The method assumes that the relationship between the radius, effective temperature, and surface gravity can be approximated using models for the internal structure and evolution of the star. The method is illustrated using the Geneva–Toulouse evolutionary computations for two metal abundances—solar and one-tenth of solar. Analysis of the systematic errors shows that the accuracy of the method is better than 10% over most part of the Hertzsprung–Russell diagram, and is about 5% for main-sequence stars. The maximum relative systematic error due to the simplifications underlying the method is about 15%. A test using eclipsing binaries confirms the viability of the proposed method for estimating stellar radii. In the region of the main sequence, systematic deviations do not exceed 2%, and the relative standard deviation is ≤4.7%. It is expected that th maximum relative error over the rest of the Hertzsprung–Russell diagram will likewise be close to the systematic error, about 15–20%. The method is applied to estimate the radii of model stellar atmospheres. Such estimates can be used to synthesize the color index and luminosity of a star. The method can be used whenever accuracies of about 10% in the estimated stellar radius and luminosity are acceptable.

Astronomy Reports. 2016;60(6):598-610
pages 598-610 views

The preventive destruction of a hazardous asteroid

Kholshevnikov K., Chechetkin V., Aleksandrova A., Galushina T., Prishchepenko A.

Аннотация

One means of countering a hazardous asteroid is discussed: destruction of the object using a nuclear charge. Explosion of such an asteroid shortly before its predicted collision would have catastrophic consequences, with numerous highly radioactive fragments falling onto the Earth. The possibility of exploding the asteroid several years before its impact is also considered. Such an approach is made feasible because the vast majority of hazardous objects pass by the Earth several times before colliding with it. Computations show that, in the 10 years following the explosion, only a negligible number of fragments fall onto the Earth, whose radioactivity has substantially reduced during this time. In most cases, none of these fragments collides with the Earth. Thus, this proposed method for eliminating a threat from space is reasonable in at least two cases: when it is not possible to undergo a soft removal of the object from the collisional path, and to destroy objects that are continually returning to near-Earth space and require multiple removals from hazardous orbits.

Astronomy Reports. 2016;60(6):611-619
pages 611-619 views