Volume 18, Issue 4
December 1997, pages 229-489
pp 229-229 December 1997
pp 231-240 December 1997
In this talk I outline some of the arguments in support of a cosmological and primordial origin of the observed microwave background radiation (MBR) in the early hot phase of the universe. This interpretation of the MBR is at the heart of the hot Big Bang model (HBBM) of the universe. The observed Planckian energy distribution of the microwave photons reflects the thermal equilibrium that can be set up naturally within HBBM in the dense early universe. Alternate interpretations face the challenge of extremely tight constraints on deviations from a Planckian distribution. Within HBBM, the formation of large scale structure is linked to tiny anisotropies in the angular distribution of the MBR photons. Recent measurements of these anisotropies seem to be broadly consistent with the predictions of the current scenarios of structure formation in the universe. Since these predictions are based on HBBM, the concurrence of data with theory provides additional support in favour of viewing the MBR as the relic of Big Bang.
pp 241-249 December 1997
With the exception ofZERO, the concept ofBIG BANG is by far the most bizarre creation of the human mind. Three classical pillars of the Big Bang model of the origin of the universe are generally thought to be: (i) The abundances of the light elements; (ii) the microwave background radiation; and (iii) the change with cosmic epoch in the average properties of galaxies (both active and non-active types). Evidence is also mounting for redshift dependence of the intergalactic medium, as discussed elsewhere in this volume in detail. In this contribution, I endeavour to highlight a selection of recent advances pertaining to the third category.
The widely different levels of confidence in the claimed observational constraints in the field of cosmology can be guaged from the following excerpts from two leading astrophysicists: “I would bet odds of 10 to 1 on the validity of the general ‘hot Big Bang’ concept as a description of how our universe has evolved since it was around 1 sec. old”-M. Rees (1995), in ‘Perspectives in Astrophysical Cosmology’CUP. “With the much more sensitive observations available today, no astrophysical property shows evidence of evolution, such as was claimed in the 1950s to disprove the Steady State theory”-F. Hoyle (1987), in ‘Fifty years in cosmology’, B.M. Birla Memorial Lecture, Hyderabad, India.
The burgeoning multi-wavelength culture in astronomy has provided a tremendous boost to observational cosmology in recent years. We now proceed to illustrate this with a sequence of examples which reinforce the picture of an evolving universe. Also provided are some relevant details of the data used in these studies so that their scope can be independently judged by the readers.
pp 251-255 December 1997
The discovery of the 3K microwave background radiation (MBR) and its interpretation as a relict of the hot big bang was probably the most important observation that led to the elevation of the hot big bang model to the status of a ‘Standard Model’. The temperature of this background is consistent with the primordial nucleosynthesis hypothesis. Detailed measurements of the spectrum and angular anisotropy of this radiation background have been found — within the measurement errors - to be consistent with the expectations of the Standard Model and with the formation of structure from the gravitational growth of primordial seed density perturbations within this framework.
pp 257-261 December 1997
I summarize the properties of the QSO absorption lines which provide evidence for the standard model of the Universe.
pp 263-269 December 1997
The detection of the Cosmic Thermal Neutrino Background (CTNB) would provide the “cleanest” evidence for the hot big bang model of the early Universe. I discuss some recent thoughts on the possibility of detecting the CTNB (especially if neutrinos have a small mass of ~ few eV) by looking for certain CTNB-induced features in the extremely high energy (E ≳ 1020 eV) cosmic neutrino spectrum that may become measurable in the future by some of the large-area extensive air-shower detectors being built for detecting extremely high energy cosmic rays.
pp 271-294 December 1997
The fundamental properties of Friedmann Universes, which are attractive because of their simplicity, are linear expansion (except for deceleration), cooling, and evolution. In addition it is assumed that the fundamental constants of physics are constant and that the known laws of physics apply (including GR). An increasing number of observational tests support these premises. In particular the expansion is as linear as can be tested. The present expansion rate (H0 = 55 ± 10 km s-1 Mpc-1) implies an expansion age of 17.8 ± 3.2 Gyr (forq0 = 0) to 11.9 ± 2.1 Gyr (for q0 = 1/2). This agrees perfectly within the errors, even for a critical Universe, with present age determinations of the oldest objects in the Galaxy which require 13.5 ± 2 Gyr.
pp 295-301 December 1997
The Galactic globular clusters are believed to be among the most ancient objects for which reliable ages can be determined. As the Universe can not be younger than the oldest object it contains, the oldest Galactic globular clusters provide one of the few most important constraints that one can have on cosmological models. Latest estimates indicate that the absolute age of the oldest globular clusters is 14 ± 3 Gyr. The calibration of absolute ages is still subject to observational and theoretical uncertainties at the ≈ 20% level, and represents a major limitation on our ability to test cosmological models. However, relative ages are starting to be much better known due to the super colour-magnitude diagrams that have been obtained through the use of CCD detectors on large telescopes and the Hubble Space Telescope. The available data are consistent with the majority of Galactic globular clusters being virtually coeval but with a minority having significantly lower ages. The existence of “prehistoric” clusters with ages of around 50 Gyr, as hypothesised in the quasi-steady state cosmology, should be readily recognised.
pp 303-311 December 1997
I review the constraints on standard big bang model arising from considerations related to structure formation. I will focus on two specific series of models though similar analysis can be performed for a wider class of models. The first one is a Ω = 1 model with non-zero cosmological constant and the second one is a Ω < 1 model with zero cosmological constant. The observational constraints which I shall discuss include the measurement of the Hubble’s constant, the ages of globular clusters, the abundance of rich clusters, the baryon content of galaxy clusters and the abundance of high redshift objects. These constraints limit the allowed range of the cosmological parameters and allow. for only a small region to survive. In particular, the aesthetically pleasing model with Ω = 1 and zero cosmological constant is ruled out by the observations. It seems necessary to fine-tune the theoretical parameters if they have to fall within the available space. This talk is based on the work in Baglaet al. (1996).
pp 313-319 December 1997
In this short contribution I want to discuss one particular candidate for the Dark Matter (DM) in the Universe, viz., the lightest supersymmetric particle (LSP). I discuss, very briefly, the motivation for Supersymmetry as well as the LSP as DM candidate. Then I summarise the current accelerator bounds on its mass and couplings and end by pointing out the implications of these limits for the experiments which search ‘directly’ for the DM.
pp 321-322 December 1997
A preferred epoch for forming galaxies argues strongly in favour of a standard Big Bang cosmology with a single epoch of creation. In this paper I present a model in which there is a causal connection between AGN activity and galaxy formation with its epoch closely linked to the observed epoch of peak AGN activity.
pp 323-333 December 1997
Still more shocking than the metaphysical assumption of some initial singularity, is the constant insistence upon the so-called cosmological principle of “homogeneity” and “isotropy” of the Universe. Observations do contradict this principle. And to me, the inhomogeneous, fractal at least on a certain scale range, of the distribution of matter is in itself an important cosmological fact, hitherto almost neglected. Moreover difficultties as to the applicability of the second principle of thermodynamics, observations of abnormal redshifts, etc., are casting large doubts not only upon the standard cosmological models, but even on the interpretation of the observed redshift as due solely to a universal expansion.
pp 335-338 December 1997
We give an elementary overview of the subject of gravitational collapse in classical general relativity. Recent theoretical evidence for the formation of black-holes and naked singularities is summarised.
pp 339-342 December 1997
The historical motivation for the Brans-Dicke theory and its connection with Mach’s principle has been discussed. Some examples of actions which can be reduced to the Brans-Dicke type have been given. Further, the recent developments in the theory in the context of inflationary cosmology have been briefly pointed out.
pp 343-347 December 1997
So far all known singularity-free cosmological models are cylindrically symmetric. Here we present a new family of spherically symmetric non-singular models filled with imperfect fluid and radial heat flow, and satisfying all the energy conditions. For larget anisotropy in pressure and heat flux tend to vanish leading to a perfect fluid. There is a free function of time in the model, which can be suitably chosen for non-singular behaviour and there exist multiplicity of such choices.
pp 349-351 December 1997
Some problems associated with the big bang cosmological model are briefly discussed. It is shown that the quasi-steady state model (QSSC) is a viable alternative. Moreover, the cosmogony related to this theory is supported by the observations.
pp 353-362 December 1997
This paper summarises the recent work on the quasi-steady state cosmology. This includes, the theoretical formulation and simple exact solutions of the basic equations, their relationship to observations, the stability of solutions and the toy model for understanding the growth of structures in the universe.
pp 363-379 December 1997
In a universe whose elementary constituents are point particles there does not seem to be any obvious mechanism for avoiding the initial singularities in physical quantities in the standard model of cosmology. In contrast in string theory these singularities can be absent even at the level where spacetime is treated classically. This is a consequence of the basic degrees of freedom of strings in compact spaces, which necessitate a reinterpretation of what one means by a very small universe. We discuss the basic degrees of freedom of a string at the classical and quantum level, the minimum size of strings (string uncertainty principle), the t-duality symmetry, and string thermodynamics at high energy densities, and then describe how these considerations suggest a resolution of the initial singularity problem. An effort has been made to keep this writeup self-contained and accessible to non-string theorists.
pp 381-387 December 1997
We briefly review the status of the “graceful exit” problem in superstring cosmology and present a possible resolution. It is shown that there exists a solution to this problem in two-dimensional dilaton gravity provided quantum corrections are incorporated. This is similar to the recently proposed solution of Rey. However, unlike in his case, in our one-loop corrected model the graceful exit problem is solved for any finite number of massless scalar matter fields present in the theory.
pp 389-392 December 1997
We explore features of a nonminimally coupled theory of scalar fields with an effective potential that supports non topological soliton solutions. It is suggested that a problem free cosmology results.
pp 393-406 December 1997
Building on evidence starting from 1966, X-ray observations have once again confirmed the association of quasars with low redshift galaxies. Enough examples of quasar-like objects ejected in opposite directions from nearby, active galaxies have accumulated so that an empirical evolutionary sequence can be outlined.
The quasars start out with low luminosity and high (z > 2) redshift. As they travel away from their galaxy of origin they grow in size and decay in redshift. The redshifts drop in steps and near the quantized values of z = 0.6, 0.3, and 0.06 the quasars become particularly active, ejecting or breaking up into many objects which evolve finally into groups and clusters of galaxies. The observations massively violate the assumptions of the Big Bang and require continuous, episodic creation in a non expanding universe of indefinitely large size and age.
pp 407-414 December 1997
One of the largest rotation curve data bases of spiral galaxies currently available is that provided by Persic& Salucci (1995; hereafter, PS) which has been derived by them from unreduced rotation curve data of 965 southern sky spirals obtained by Mathewson, Ford& Buchhorn (1992; hereafter, MFB). Of the original sample of 965 galaxies, the observations on 900 were considered by PS to be good enough for rotation curve studies, and the present analysis concerns itself with these 900 rotation curves.
The analysis is performed within the context of the hypothesis that velocity fields within spiral discs can be described by generalized power-laws. Rotation curve data was found to impose an extremely strong and detailed correlation between the free parameters of the power-law model, and this correlation accounts for virtually all the variation in the pivotal diagram. In the process, the analysis reveals completely unexpected structure which indicates that rotation curves can be partitioned into well-defined discrete subclasses.
pp 415-433 December 1997
Evidence for redshift quantization is reviewed and summarlized. The cosmic background rest frame appears to be central to the effect. Periods are consistently found to be members of a set predicted by the ninth-root Lehto-Tifft rule which has implications relating to the possible nature of time, particle physics and cosmology. Galaxies can be divided into four morphological families associated with particular classes of periods. Numerous examples are given including recent work where redshifts appear to show evidence of changes between related quantized levels.
pp 435-440 December 1997
The variable Mass Hypothesis of conformal gravitation theory of Hoyle-Narlikar is used to develop a model for the anomalous redshift quasar-galaxy associations. It is hypothesised that quasars are born in and ejected from the nuclei of parent galaxies as massless objects and the particle masses in them systematically increase with epoch. The dynamics of such an ejection is discussed and it is shown that the observed features such as redshift bunching and quasar alignments can be understood in this scenario. Further tests of this hypothesis are suggested.
pp 441-447 December 1997
There have been claims, from time to time that there are periodicities in the redshift distribution of quasistellar objects. These claims are examined from various statistical angles for the 2164 QSO redshifts available in the latest compilation by Hewitt& Burbidge (1990). The statistical tests reveal moderate to strong evidence for periodicities ξ = 0.0565 and 0.01270-0.129.
pp 449-454 December 1997
The paper shows that a phenomenological model of inertial induction based on a proposed extension of Mach’s Principle can produce the observed cosmological red shift in a quasi-static infinite universe. Unlike all other theories (except the Doppler effect) to explain the observed red shift this model can be verified from other local effects predicted by this mechanism. A number of such phenomena have been investigated and these expected effects are not only found to be present but they also explain a number of unexplained or ill explained observational results. It is suggested that attempts should be made to verify the model through further tests and observations.
pp 455-463 December 1997
The current status of a continuing programme of tests for redshift periodicity or ‘quantization’ of nearby bright galaxies is described. So far the redshifts of over 250 galaxies with high-precision HI profiles have been used in the study. In consistently selected sub-samples of the datasets of sufficient precision examined so far, the redshift distribution has been found to be strongly quantized in the galactocentric frame of reference. The phenomenon is easily seen by eye and apparently cannot be ascribed to statistical artefacts, selection procedures or flawed reduction techniques. Two galactocentric periodicities have so far been detected, ∼ 71 .5km s-1 in the Virgo cluster, and ∼37. 5km s-1 for all other spiral galaxies within ∼ 2600km s-1. The formal confidence levels associated with these results are extremely high.
pp 465-475 December 1997
pp 477-489 December 1997
Volume 40 | Issue 2
Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.