Advances in Astronomy and Space Physics, 2015, вип. 1

Dynamics of dark energy in collapsing halo of dark matter

2017-06-10T00:03:20Z

Dynamics of dark energy in collapsing halo of dark matter Tsizh, M.; Novosyadlyj, B. We investigate the non-linear evolution of spherical density and velocity perturbations of dark matter and dark energy in the expanding Universe. For this we have used the conservation and Einstein equations to describe the evolution of gravitationally coupled inhomogeneities of dark matter, dark energy and radiation from the linear stage in the early Universe to the non-linear stage at the current epoch. A simple method of numerical integration of the system of non-linear differential equations for evolution of the central part of halo is proposed. The results are presented for the halo of cluster (k = 2 Mpc⁻¹ ) and supercluster scales (k = 0.2 Mpc⁻¹ ) and show that a quintessential scalar field dark energy with a low value of effective speed of sound cٍ < 0.1 can have a notable impact on the formation of large-scale structures in the expanding Universe.

Fast radio bursts as electromagnetic radiation from cusps on superconducting cosmic strings

2017-06-10T00:03:19Z

Fast radio bursts as electromagnetic radiation from cusps on superconducting cosmic strings Zadorozhna, L.V. Cosmic strings are topological defects, relicts of the early Universe, which can be formed during phase transitions of fields with spontaneous broken symmetry. There also exists a special class of cosmic strings - superconducting cosmic strings, inside of which the massless charge carriers, so-called zero modes, are presented and can move along the string without any resistance. The superconducting cosmic strings during their relativistic motion through the cosmic plasma could be a powerful source of electromagnetic radiation. The emission of cusps on the superconducting strings is highly beamed and has the nature of bursts. In the present work, it is shown, that the millisecond extragalactic radio bursts, discovered during the last decade, called the fast radio bursts (FRB), with unknown nature, could be explained as radiation from cusps on superconducting cosmic strings. Estimates made for ten FRBs discovered till now show that bursts could be produced by a string with α = ΓGµ/c² ∼ 5 · 10⁻¹³ − 10⁻¹², where Γ ∼ 50 is a dimensionless parameter, G is the gravitational constant, c is the speed of light, µ is the mass per unit length of a string, which corresponds to the energy scale of the phase transition η ∼ 1.2 · 10¹² − 1.7 · 10¹² GeV. The observed duration, flux and event rate are in a good agreement with the proposed model. In the framework of emission from cusps of superconducting cosmic string loops, probability of FRB detecting is estimated, which is found to be highly close to the probability of detecting, given by observational data.

Nitrogen abundance in the Blue Compact Dwarf galaxies from SDSS

2017-06-10T00:03:13Z

Nitrogen abundance in the Blue Compact Dwarf galaxies from SDSS Vovk, K.B. We examined all of the galaxies in the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) to select those with a dete ted [O ΙΙΙ ] λ4363 emission line, whih allows to derive electron temperatures in H װ regions and element abundan es by the diret method. We selected two sub-samples of galaxies: one with detected WR features in their spectra, and the other with the nebular He װ λ4686 emission line. We confirm the increase of the N/O abundance ratio with decrease of the equivalent width EW(Hβ) of the Hβ emission line. This result is explained by gradual nitrogen enrihment of the interstellar medium by ejecta from massive stars in the most recent starburst episode.

Geometry of highly inclined protoplanetary disks

2017-06-10T00:03:25Z

Geometry of highly inclined protoplanetary disks Zakhozhay, O.V.; del Burgo, C.; Zakhozhay, V.A. We present a geometric model for the modelling of spectral energy distribution of inclined protoplanetary disks. We investigate peculiarities in the geometry of nearly edge-on disks with an inner hole and a central object. In the investigation we consider two cases: that of geometrically thin disks (where the star is larger than the rim of the inner edge of the disk) and that of eometrically thick disks (when the star is smaller than the inner rim of the disk). Our model is appropriate for modelling substellar objects with primordial gas-rich disks, as activity (such as accretion or outflows) in such disks has low amplitude and can be ignored even when modelling early evolution stages. Furthermore, it can also be used to model any symmetric system with a disk and a spherical central body (star, brown dwarf or giant planet).