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  • Other Sources  (5)
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  • 1
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    The growth of density perturbations in radiative shocks (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The paper presents a new investigation of the growth of thermal instabilities behind radiative shocks. The analytic and numerical results disagree with McCray, Stein, and Kafatos, who were attempting to explain the filamentary structure commonly seen in supernova remnants, and proposed that the growth of density perturbations would lead to gross condensations in the postshock cooling region. Hydrodynamical simulations are generated which corroborate arguments in favor of no growth in the long-wavelength limit. These simulations also agree with a renewed analytic approach in the short-wavelength limit, and show that the region of rapid growth will remain inconspicuous in the overall density rise toward the back of the shock. It is noted that these calculations are in accord with some recent observations of supernova remnants where the observed filaments do not seem to have been produced by any local thermal instability process.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 345; 853-861
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  • 2
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    X-ray emission from reverse-shocked ejecta in supernova remnants (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A simple physical model of the dynamics of a young supernova remnant is used to derive a straightforward kinematical description of the reverse shock. With suitable approximations, formulae can then be developed to give the X-ray emission of the reverse-shocked ejecta. The results are found to agree favorably with observations of SN1006.
    Keywords: ASTROPHYSICS
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  • 3
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    Overpressured cocoons in extragalactic radio sources (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: It is shown that the cocoons of shocked gas which surround powerful double radio sources can have significantly higher pressures than the surrounding intergalactic medium. The pressures can be high enough to confine the jets in these sources, obviating the need for magnetic confinement. The cocoon pressure and the age of a radio source may be estimated from observable quantities, as demonstrated here for the radio galaxy Cygnus A. It is suggested that overpressured cocoons in high-redshift radio galaxies engulf and compress circumgalactic clouds, driving them over the Jeans limit and triggering star formation. It is proposed that this process leads to the observed alignments of optical continuum emission with radio source axes.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 345; L21-L24
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  • 4
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    Simulations of the supernova-dominated interstellar medium in disk galaxies (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A three-dimensional simulation of the evolution of an SNR-dominated ISM from an initially homogeneous, uniform substrate is presented. Systems with only bremsstrahlung cooling are compared with those cooled by radiation from metals. This distinction translates into a size difference in the resulting SNRs, and thus in the ability of isolated SNRs to affect the evolution of the galactic ecosystem. At a given SN rate, correlating the SNe decreases the global evolution of the galaxy if the SNRs individually can affect the system. It is shown that, when the density of the ISM varies widely, the N(R) test can give the reverse of standard expectations. It is shown that strong SNRs can impede interstellar tunnel production because of their ability to transport material and fill a previously evacuated volume, and that cloud size affects the final picture of the system.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 367; 96-114
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  • 5
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    The evolution of cocoons surrounding light, extragalactic jets (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: If the mass density of supersonic, collimated material is less than that of the surrounding medium, a so-called light jet will be enveloped by a cocoon of overpressured shocked gas. Hydrodynamical simulations are used to understand the evolution of the cocoon. The cocoon's evolution is also compared to a simple analytic theory. To reconcile the theory with the simulations, the growth of the jet head must be taken into account. The overpressured cocoon stage exists for a relatively short astronomical time, after which only the region of the cocoon near the jet head remains overpressured. The spatial distribution of the optical emission often observed in distant extragalactic jet systems can be explained with this improved understanding of cocoon evolution.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 392; 2 Ju; 458-464
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