Advances in Astrophysics

14

Authors: Denis Michel

The relationships between the redshifts, the luminosity distance and the true distances at the times of light emission and reception, are formally calculated in Euclidean spaces whose expansion is describable using simple functions: proportional to cosmic time, power law or exponential, and for the different assumptions about the origin of the redshift: kinematic, relativistic and wave stretching effects. None of these combinations gives the same results in terms of redshift, of horizon, of distances and of deviation from the Hubble law. This systematic analysis provides the limit cases of expansion scenarios.

4

Authors: V.G. Mete

This paper deals with the study of five dimensional non – static plane symmetric cosmological model within the framework of Lyra's manifold when the source of the gravitational field is perfect fluid with pressure equal to energy density. The cosmological solutions have been analyzed through various physical and geometrical properties.

13

Authors: Göran Henriksson

To get accurate knowledge about the longitudinal motion of the Moon we must use the oldest preserved interpretable depictions and texts from the ancient cultures. 33 ancient total or almost total solar eclipses, back to 3653 BC, have been used to determine the lunar sidereal secular acceleration in longitude, -30.128 ±0.0035 arcseconds/(century)2 ("/cy2). The lunar secular acceleration, from the Lunar Laser Range (LLR) measurements, -25.856 ±0.003 "/cy2, must be corrected for the relativistic effect, -3.604 "/cy2, in the Earth-Moon inertial system, to get the lunar sidereal secular acceleration, –29.460 "/cy2, corrected for General Relativity. The difference between this value and the new calibration, -0.668 ±0.0046 "/cy2, may be interpreted as the cosmological acceleration by Dvali et al. in a Modified Theory of gravity. This value is equivalent to a Mass of the Graviton = 1.306 ±0.009 x 10-56 grams and there is no need for the hypothetical Dark Energy.

8

Authors: H. Shanjit, K. Yugindro Singh

In this work, the geodesic equations of motion of a test particle in the Kerr-Newman (KN) anti de Sitter spacetimes are presented in the light of the Hamiltonian-Jacobi formalism. We have examined, in the frame of KN anti de Sitter spacetimes, the spherical and circular orbits that the test particle may describe in a rotating charged black hole, discarding the gravitational and electromagnetic radiation and found that bounded spherical and circular stable orbits can exist in the regions of 0 < r < r− in which r− is the inner event horizon of the black hole.

10

Authors: Lorenzo Zaninetti

In this paper we present formulae for chord length distribution in the framework of Poissonian Voronoi Tessellation (PVT) and non Poissonian Voronoi Tessellation (NPVT). The introduction of the scale parameter in the obtained distributions allows us to model the chord for cosmic voids. A graphical comparison between cosmic voids visible on two catalogs of galaxies, 2dFGRS and VIPERS, and theoretical random chords is reported.

12

Authors: Halife Caglar, Sezgin Aygün

In this paper we have researched higher dimensional flat Friedmann-Robertson-Walker (FRW) cosmological model solutions for string cloud and domain walls coupled with quark and strange quark matters in Lyra and Riemann geometries. We have obtained that string tension density is zero in Lyra and Riemann geometries. Also, the displacement field vector behaves like a cosmological constant in our models. In addition to these, some physical and kinematical quantities have been generalized and discussed in Lyra and Riemann geometries. Also our results are consistent with the results of Yılmaz, Back et al. and Adcox et al. in four dimensions.

55

Authors: O. Rahman

A theoretical investigation has been carried out for understanding the nonlinear propagation characteristics of the dust-ion-acoustic (DIA) solitary and shock waves in an unmagnetized dusty plasma containing Maxwellian negative ions, superthermally distributed electrons, positively charged stationary dust particles and cold mobile inertial positive ions. The reductive perturbation method has been employed to derive the Korteweg-de Vries (K-dV), modified Korteweg-de Vries (mK-dV) as well as Burger equations along with its solutions in order to study the basic features of such waves both numerically and analytically. It has been found that the presence of superthermal electrons significantly modifies the basic properties of such DIA solitary and shock wave structures. The present investigation can be very effective for understanding and studying various astrophysical environments (viz. Saturn magnetosphere, pulsar magnetosphere, etc).

8

Authors: H.-J. Fahr, M. Heyl

According to present cosmological views, the energy density of CMB (Cosmic Microwave Background) photons, freely propagating through the expanding cosmos, varies proportional to 1/S4 with S being the scale factor of the universe. This behavior is expected because General Theory of Relativity, in application to FLRW- (Friedmann-Lemaitre-Robertson-Walker) cosmological universes, leads to the conclusion that the photon wavelengths increase during their free passage through the spacetime metrics of the universe by the same factor as does the scale factor S. This appears to be a reasonable explanation for the presently observed Planckian CMB spectrum with its actual temperature of about 2.7 K, while at the time of its origin after the last scattering during the recombination phase its temperature should have been about 3000 K, at an epoch of about 380 ky after the Big Bang, when the scale of the universe Sr was smaller by roughly a factor of S/Sr = 1 + zr = 1100 compared to the present scale S = S0 of the universe. In this paper we start from putting the question whether the scale-behavior of the CMB energy density that enters the energy-momentum tensor of the field equations describing the expanding universe is really falling off like S −4 and, if in fact a deviation from a behavior according to S −4 would occur, why do we nevertheless presently observe a CMB energy density which appears to be in accordance with such a S −4 -scaling? This question arises from another basic and fundamental question, namely: Can we really assume that the wavelength of the freely propagating photon during its travel all the way along its light geodetic is permanently affected by the expansion of the universe, i.e continuously recognizes the expansion of the cosmic scale S? With other words: Do freely propagating photons really undergo a permanent change of their wavelengths when freely traveling through cosmic space-time or is the observationally apparent energy loss of cosmologically red-shifted photons an effect which only occurs just in the moment of photon registration at some specific world point? If the latter would prove to be true , then it would mean that the energy density of freely propagating, non-interacting CMB photons, due to non-changing, conserved wavelengths, is behaving with respect to cosmic scale variation different from conventional expectations, but rather would turn out to behave just like the energy density of matter, namely according to S −3 . Hence the photon part of the energy momentum tensor would become different and associated solutions of FLRW-equations would undergo corresponding modifications. In consequence, the CMB energy density as far as it enters the energy-momentum tensor generated by freely propagating CMB photons during the expansion period of the universe after the recombination era would no longer become negligible for the cosmic dynamics, since its value would stay in the same order of magnitude as that of baryonic or dark matter.

13

Authors: A. Safiya Beevi, Ram Krishan Sharma

The motion of a particle in the restricted three-body problem is explored by treating the more massive primary as an oblate spheroid with its equatorial plane coincident with the plane of motion of the primaries using a perturbation method. Initial conditions for the infinitesimal periodic orbits around the more massive primary are generated and the effect of oblateness on the perigee of these orbits is studied as well. It is observed that when oblateness coefficient is increased, the perigee of the orbit shifts towards both the primaries depending upon the increase in period and mass ratio. It is further noticed that during this transition, for certain periods, the perigee of the orbit remains unaltered with the increase in the oblateness coefficient.

17

Authors: Nishanth Pushparaj, Ram Krishan Sharma

Photogravitational Restricted Three-Body Problem (PRTBP) with smaller primary being an oblate spheroid with its equatorial plane coincident with the plane of motion of the primaries is considered and halo orbits in the vicinity of Sun-Mars Lagrangian points L1 and L2 are computed numerically. The effects of perturbations on size, shape, location and time period of the halo orbits are studied. It is found that the increase in solar radiation pressure at constant oblateness elongates the halo orbits at L1 and the orbits move towards the radiating body. At L2, the halo orbits shrink and move towards the smaller primary with increase in solar radiation pressure at constant oblateness. For constant radiation pressure, increase in oblateness causes the location of L1 and L2 halo orbits to move away from the smaller primary. The time period of L1 halo orbits increases with increase in radiation pressure for constant oblateness and decreases with increase in oblateness for constant radiation pressure. However, the effect of solar radiation pressure and oblateness for L2 halo orbits is reversed.