• Volume 7, Issue 1

      March 1986,   pages  1-51

    • The neutrino hypothesis for dark matter in dwarf spheroidals

      Ramnath Cowsik

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      The theoretical expectation of the high mass of >400 eV for the particles constituting the dark matter in dwarf-spheroidals as an artifact of the implicit assumption that the density of particles vanishes at the visible edge. On the contrary if our Galaxy and the dwarf-spheroidals are embedded in a neutrino condensation of the dimensions of the cluster thenm- 10 eV can accommodate all the observations.

    • Dynamical effects of an extended cloud of dark matter on dwarf spheroidals

      Ramanath Cowsik Pranab Ghosh

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      If the dwarf spheroidals are embedded in an extended cloud of dark matter then their density profiles can be reproduced by assuming a Maxwellian distribution of velocities for the constituent stars. The observed luminosity profiles of dwarf spheroidals imply densities for the dark matter in the range 10-26 to 10-25 g cm-3, and mass-to-luminosity ratios which are typically an order of magnitude greater than those of globular clusters. Neutrinos of mass ∼ 10 eV and (v) ∼ 1000 km s-1 can provide this requisite density for the background.

    • Towards a physical model for galactic rotation curves

      Ramanath Cowsik Pranab Ghosh

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      Extensive and meticulous observations of the rotation curves of galaxies show that they are either flat or gently going up, but rarely decreasing, at large galactocentric distances. Here we show that the gravitational potential which would lead to such rotation curves arises naturally when the visible matter modelled as a collisionless Maxwellian gas is embedded in a dark halo of collisionless particles with a much higher dispersion in velocities.

    • Dark matter-systematics of its distribution

      R. Cowsik M. Vasanthi

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      The dynamical masses of dwarf-spheroidals, spiral and elliptical galaxies, dwarf irregular binaries, groups of galaxies and clusters are shown to lie in a band about the M ∼ ρR3line. The value of ρ is approximately the same as that estimated for unseen matter in the solar neighbourhood. The clusters themselves lie about theM ∼ R-3line derived for a self-gravitating neutrino gas; their masses are distributed around the maximum Jeans-mass, MJmax. corresponding to mv - 10 eV in an expanding universe. The present day length scales of clusters and the dispersion in the velocities observed within them are understood in terms of a 100-fold expansion subsequent to the initial growth of the fluctuations at MJmax. These systematics on theR-M plane imply that the initial condensations in the expanding universe are on the scale of the rich clusters of galaxies, these condensations were triggered dominantly by the gravitation of the neutrinos and the constant density of al systems arises naturally due to the embedding of these systems in the large scale neutrino condensations. If the neutrino density falls off asr-2 beyond the cluster edge till the distributions from different clusters overlap, then the mean density of the neutrinos approximately equals the closure density of the universe.

    • Energy loss of electrons in solar atmosphere taking many-body interactions into account

      K. L. Moza P. K. Koul R. R. Rausaria P. N. Khosa

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      Role of many-body interactions on the energy loss of electrons accelerated at neutral point during solar flares has been studied. Energy loss with and without many-body interactions has been computed for different electron-density models as function of height. The energy loss increases by a factor of two by inclusion of many-body interactions for incident electron energies greater than 10 keV. Role of this on the generation of hard X-rays is discussed.

    • The identity of the primary component of capella

      R. & R. Griffin

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      Ever since the discovery in 1899 that Capella is a double-lined spectroscopic binary system the sharp-lined component, which has the later spectral type, has always been regarded as the primary (more luminous) star. However, traces obtained with radial-velocity spectrometers show that the broad-lined, earlier-type component is actually the primary.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      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.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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