Professor Jayant V. Narlikar

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Subject: search.filters.subject.Astronomical models

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    Counter images in closed elliptical friedmann universes
    (American Astronomical Society, 1985-01-06) Narlikar, J. V.; Seshadri, T. R.
    It is shown that the different connectivity implied by the elliptical version of a closed Friedmann model allows two images of a distant astronomical object to be seen, provided the deceleration parameter q0 of the Friedmann model exceeds unity. Of the two images the direct image is along the shortest-route light track. If the redshift of the direct image exceeds (1.5q0 - 1)/(q0 - 1)sq then a second counterimage should be visible at the diametrically antipodal position. The direct image has a maximum possible redshift, and it is suggested that the apparent cutoff in the redshifts of QSOs may be due to this effect. Other observable consequences of this result are discussed in relation to galaxies and QSOs.
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    Quasars Q 2345 + 007 A,B and 3C 273 : Gravitational Lenses?
    (Liege University Press, Liege, 1983-01-14) Narlikar, J. V.; Subramanian, Kandaswamy; Narasimha, D.; et al.
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    Quantum cosmology as a cure of three ailments of classical cosmology
    (Astronomical Society of India, 1983-08-12) Padmanabhan, T.; Narlikar, J. V.
    The standard big bang models of classical cosmology are known to possess three defects. The oldest known defect is spacetime singularity whose existence seems inevitable within the classical framework. The second defect is the existence of a particle horizon which severely limits communications across the distant parts of the universe whose observed homogeneity therefore becomes inexplicable. Recently a third defect has been highlighted, viz., the required fine tuning of the early universe close to the flat spatial model in order to account for the present range of its mean density. We show before that the injection of quantum ideas holds out hope of a cure for all the three ailments described above. Using a simple path integral formalism for quantum cosmology we present arguments which suggest that (i) it is extremely unlikely that the universe evolved to the present state from quantum states of singularity and particles horizon;(ii) of all the possible Robertson-Walker models that could evolve our of quantum fluctuations of the empty Minkowski universe the flat model is overwhelmingly probable.
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    Single exhaust model for backward emission in doppler quasars
    (American Astronomical Society, 1983-10-01) Narlikar, J. V.; Subramanian, Kandaswamy
    This paper provides an astrophysical scenario for Hoyle's (1980) conjecture that quasars ejected at high velocities from active galactic nuclei predominantly radiate in a narrow backward cone. Through such backward emission, local Doppler theory can explain the fact that no blueshifted quasars are seen. It is held that a fast moving quasar encounters a strong ram pressure from the intergalactic medium in the forward direction which suppresses the forward exhaust. Attention is given to the hydrodynamic, gravitation theory, and radiation requirement constraints on the model, which is shown to accommodate them over a comfortable range of parameters, and which also helps in the understanding of some of the observable properties of quasars.
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    Contribution of quasistellar objects to the cosmic X-ray background
    (Indian Institute of Astrophysics, 1983-01-14) Narlikar, J. V.; Burbidge, G.
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    Empirical approach to cosmology
    (Springer, 1981-01-23) Narlikar, J. V.; Burbidge, G.
    A two-component model of the universe is proposed, based on the observations of discrete extragalactic sources and the microwave background radiation. The large scale dynamics of the universe is determined by the radiation component and it leads to a characteristic size of the universe of approximately 600,000 Mpc and an age of approximately one trillion years. The second component, that of matter, occurs in discrete sources which group together in super-superclusters of characteristic size approximately 6000 Mpc and age 10 billion yr. It is suggested that the Galaxy belongs to one of these super-superclusters and that observations of discrete sources are confined to this unit. A reasonable agreement with the cosmological tests is obtained on the assumption that the geometry within a typical super-supercluster is Euclidean and that the redshifts of galaxies arise from a Doppler effect due to motions originating in a local explosion which gave birth to the super-supercluster. Further observational checks on this model are proposed.
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    Applications of statistical techniques to the angular size-flux density relation for extraglactic radio sources
    (Willy-Blackwell, 1977-01-14) Narlikar, J. V.; Chitre, S. M.
    The data on the angular sizes (theta) and flux densities (S) of extragalactic radio sources selected from two surveys are subjected to two independent statistical tests in order to determine whether the data warrant the conclusion that the universe is evolving. The nature of the observed scatter in the (theta, S) relation is examined, and a minimum chi-squared test is used to compare the observed (theta, S) plot with three theoretical models (one evolutionary and two nonevolutionary). A median test is then applied to compare the median angular sizes of two source samples in a narrow range of flux density. The results obtained indicate that due to the existing large scatter in the (theta, S) data, it is not possible to distinguish clearly between the evolutionary and the nonevolutionary models.