Research Papers (JVN)

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Author: search.filters.author.Narlikar, J. V.Subject: search.filters.subject.Quasars

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Now showing 1 - 10 of 17
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    Luminosity volume test and the local hypothesis of quasars
    (Indian Academy of Sciences, 1986-01-28) Hoyle, F.; Narlikar, J. V.
    It is shown that the luminosity-volume test for optically selected objects has an in-built bias towards increasing the average value of V/Vm above the Euclidean value of 1/2. A more satisfactory bias-free statistic is suggested in the form of In (V/Vm), The result of applying the test to a sample from the Bright Quasar Survey (BQS) shows that the local hypothesis of quasars is consistent with the data.
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    Backward emission in quasars
    (Indian Academy of Sciences, 1985-11-29) Narlikar, J. V.
    In the local Doppler theory of quasars the lack of observed blueshifts can be explained if quasars, ejected at high velocities from active galactic nuclei, radiate predominantly in a backward cone. An astrophysical single exhaust model has been proposed which not only explains why quasars emit radiation in the backward direction, but may also be able to account for some of their morphological features.
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    Statistical significance of a large quasar inhomogeneity in the sky
    (EDP Sciences, 1985-05-09) Narlikar, J. V.; Subramanian, Kandaswamy
    Statistical techniques are devised to study the significance of apparent inhomogeneities in the distribution of points on a spherical surface, especially in the form of jets and chains. The methods are applied to complete samples of radio quasars in specific windows of magnitudes and redshifts. It is found that while most of the distributions studied show very little evidence of non-randomness, the inhomogeneity reported by Arp (1984) is highly significant. There is also some evidence, although a statistically weaker one, for a chainlike structure in the distribution of low redshift quasars in another area of the sky.
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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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    3C 273 : A gravitationally lensed quasar?
    (EDP Sciences, 1984-05-30) Chitre, S. M.; Narasimha, D.; Narlikar, J. V.; et al.
    It is suggested that the abnormal brightness of the quasar 3C 273, coupled with the observations of superluminal motions in its radio core B as well as the misalignment of its VLBI jet with the optical jet, can be understood by postulating a faint spheroidal lensing galaxy located about halfway along the line of sight to the quasar. The lens model also helps to understand why the quasar is found slightly off-centre with respect to its nebulosity. The probability for such a lens system to arise for 3C 273 by chance is shown to be no less than that computed on the basis of the relativistic beaming hypothesis. Further tests of the lens model are discussed.
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    Faster-than-light motion in quasars
    (Indian Academy of Sciences, 1984-07-27) Narlikar, J. V.; Chitre, S. M.
    Over the past fifteen years, observations of some quasars with the techniques of very-long-baseline interferometry have shown that the angular separation between pairs of radio-emitting regions in their cores is increasing year after year. If the quasars are indeed as far away as implied by Hubble’s law, then these angular motions translate into linear speeds several times the speed of light. Several theoretical scenarios have been proposed to show that the observed motions are illusory. The leading contender in this field—the relativistic beam model—and an alternative offered by the concept of a gravitational screen are described and compared in the light of recent observational data.
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    Radiation backgrounds and their cosmologival implications
    (T.I.F.R., 1983-01-15) Narlikar, J. V.
    The information content of radiation backgrounds at wavelengths ranging from radio waves to gamma rays is reviewed, within the context of the standard big bang cosmology. It is shown that the various backgrounds provide useful inputs and constraints on the physical features of the universe such as the existence and growth of large scale inhomogeneities like galaxies, clusters and superclusters, the overall density of the universe, the photon to baryon ratio and the extent of antimatter in the universe, etc. It is argued that there are questions posed by the data which may require rethinking of some aspects of standard cosmology.
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    Single exhaust model for backward emission in fast moving quasars
    (Liege University Press, Liege, 1983-01-01) Subramanian, Kandaswamy; Narlikar, J. V.
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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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    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.