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  • Articles  (82)
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  • 1
    Electronic Resource
    Electronic Resource
    Orbits of short period comets captured from the Oort cloud (1996)
    Springer
    Earth, moon and planets 72 (1996), S. 45-50 
    Details
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Oort cloud comets occasionally obtain orbits which take them through the planetary region. The perturbations by the planets are likely to change the orbit of the comet. We model this process by using a Monte Carlo method and cross sections for orbital changes, i.e. changes in energy, inclination and perihelion distance, in a single planet-comet encounter. The influence of all major planets is considered. We study the distributions of orbital parameters of observable comets, i.e. those which have perihelion distance smaller than a given value. We find that enough comets are captured from the Oort cloud in order to explain the present populations of short period comets. The median value of cos i for the Jupiter family is 0.985 while it is 0.27 for the Halley types. The results may explain the orbital features of short period comets, assuming that the active lifetime of a comet is not much greater than 400 orbital revolutions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00117502
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  • 2
    Electronic Resource
    Electronic Resource
    Near-Earth populations of bodies coming from the Oort cloud and their impacts with planets (1995)
    Springer
    Earth, moon and planets 71 (1995), S. 219-223 
    Details
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract When Oort cloud comets enter the planetary region their orbital evolution is dominated by encounters with the planets. Some of them become short period comets and enter the terrestrial planetary region to form a potential source of cratering. We have computed the orbital evolution of comets by encounters with the seven major planets. We find 0.5–2 impacts/Myr on the Earth, somewhat lower than the observed rate of about 2.8 impacts per Myr causing craters ≥ 20 km in diameter. Thus as far as numbers go, it is quite possible that dead comets are a major, even if not the dominant source of cratering on the Earth. We have also tested how well the expected variations in the Oort cloud comet flux show up in the rate of impacts. We find that the periodicity is reflected also in the cratering rate, though with a time delay and with added noise.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00612962
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  • 3
    Electronic Resource
    Electronic Resource
    Monte Carlo Simulations of Oort Cloud Comets: the Influence of Mantle Blow-off on the Inclination Distribution of Jupiter Family (1997)
    Springer
    Earth, moon and planets 77 (1997), S. 239-244 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; Jupiter family ; simulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We have developed an efficient Monte Carlo method by which we can evaluate the evolution of comets. There are many poorly known evolutional parameters, and we have investigated the influence of these parameters on the final populations and the inclination distributions of short-period comets. We compare the observed and calculated inclination distributions of different comet populations and obtain a good fit for the inclinations of the Jupiter family comets by assuming a mantle blow-off and a sudden brightening of the comet when its perihelion distance is lowered in a major jump.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006281618542
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamical friction on a satellite of a disk galaxy: The circular orbit (1990)
    Springer
    Celestial mechanics and dynamical astronomy 48 (1990), S. 95-113 
    Details
    ISSN: 1572-9478
    Keywords: Dynamical friction ; satellite galaxy ; disk galaxy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In a previous paper, we have studied dynamical friction during a parabolic passage of a companion galaxy past a disk galaxy. This paper continues with the study of satellites in circular orbits around the disk galaxy. Simulations of orbit decay in a self gravitating disk are compared with estimates based on two-body scattering theories; the theories are found to give a satisfactory explanation of the orbital changes. The disk friction is strongly dependent on the sense of rotation of the companion relative to the rotation of the disk galaxy as well as on the amount of mass in a spherical halo. The greatest amount of dynamical friction occurs in direct motion if no spherical halo is present. Then the infall time from the edge of the disk is about one half of the orbital period of the disk edge. A halo twice as massive as the disk increases the infall time four fold. The results of Quinn and Goodman, obtained with a non-self-gravitating method, agree well with our experiments with massive halos (Q 0 ≈ 1.5), but are not usable in a more general case. We give analytic expressions for calculating the disk friction in galaxies of different disk/halo mass ratios.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00049508
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  • 5
    Electronic Resource
    Electronic Resource
    Anisotropic gravitational radiation in the problems of three and four black holes (1995)
    Springer
    Celestial mechanics and dynamical astronomy 62 (1995), S. 377-394 
    Details
    ISSN: 1572-9478
    Keywords: Black holes ; binary ; gravitational radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The momentum flux in merging binary black holes is rediscussed using the actual orbit integrations. The terminal velocity acquired by the centre of mass of the system is found to be greater than the estimate of Fitchett (1983) by a factor of 1.45. The actual value in km s−1 is still uncertain but may be as high as 2000 km s−1. The centre of mass velocity kick at a black hole merger is incorporated in the orbit integration of few black hole systems. Assuming that the symmetric break-up mode of such systems corresponds to the classical double radio sources, we determine that the centre of mass velocity kick can be about 1000 km s−1 at most.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00692287
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  • 6
    Electronic Resource
    Electronic Resource
    Leading spiral arms, retrograde galaxy encounters and massive halos (1988)
    Springer
    Celestial mechanics and dynamical astronomy 45 (1988), S. 31-36 
    Details
    ISSN: 1572-9478
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study, theoretically and with N-body simulations, the formation of spiral patterns in retrograde galaxy encounters. A one-armed leading spiral dominates in a disk if the tidal perturbation from the companion is large and the disk is surrounded by a massive halo. Otherwise, a trailing pattern forms. The leading arm is made up of particles in slightly elongated orbits whose turning points outline the arm. The arm rotates opposite to the disk rotation. We have found one spiral galaxy, NGC4622, with a leading arm near its nucleus. From the literature, we find that very few spirals, if any, in a sample of strongly perturbed galaxies have leading arms. A possible reason for this is that few spiral galaxies have a halo with larger mass than the disk within the visible disk.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01228973
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  • 7
    Electronic Resource
    Electronic Resource
    The problem of few black holes (1989)
    Springer
    Celestial mechanics and dynamical astronomy 46 (1989), S. 277-285 
    Details
    ISSN: 1572-9478
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The problem of few black holes becomes important in multiple mergers of galaxies. If supermassive black holes in centres of galaxies are common, then interaction of three or four supermassive black holes should also be common. The merger of two galaxies with one black hole each produces a semi-stable black hole binary system. Subsequent mergers of galaxies with their own central black holes produces dynamical few-body evolution in which mergers of black holes occur. According to our numerical simulations this evolution typically ends when only one or two black holes remain and, in the latter case, they are ejected in opposite directions from the center of the galaxy. Even when we pick the initial black hole masses at random from a wide distribution, the two black hole ejections happen rather symmetrically. Sometimes the final masses differ considerably in which case only the lighter black hole is ejected. This is caused by the potential barrier of the galaxy itself which prevents the heavy slowly moving black hole flying out of the galaxy. We discuss OJ287 as a possible example of a multiple black hole system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00049262
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  • 8
    Electronic Resource
    Electronic Resource
    On construction of analytic solutions to the three body problem by use of computer experiments (1988)
    Springer
    Celestial mechanics and dynamical astronomy 45 (1988), S. 37-43 
    Details
    ISSN: 1572-9478
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract New analytic approximations of the general three-body problem are given. They are obtained by making use of approximate analytic theory as well as 26000 computed orbits. These solutions give the energy of the binary after the three-body system has broken up, or alternatively the terminal velocity of the escaping body. It is shown that the hard binary scattering and the break-up of bound three-body systems are described by the same analytic expression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01228974
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  • 9
    Electronic Resource
    Electronic Resource
    Formation of leading spiral arms in retrograde galaxy encounters (1989)
    Springer
    Astrophysics and space science 156 (1989), S. 205-208 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study, theoretically and withN-body simulations, the formation of spiral structures in retrograde galaxy encounters. A one-armed leading spiral dominates in a disc if (i) the tidal perturbation from the retrograde companion is large enough, and (ii) the disc is surrounded by a massive halo. From the literature we find that very few spirals in a sample of galaxies with a large companion have leading spiral arms. A possible reason for this is that very few spiral galaxies have a halo with a larger mass than the disc mass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00646367
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  • 10
    Electronic Resource
    Electronic Resource
    Three-body gravitational scattering: Comparison between theory and experiment (1979)
    Springer
    Celestial mechanics and dynamical astronomy 19 (1979), S. 53-58 
    Details
    ISSN: 1572-9478
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Three-body gravitational encounters are thought to be an important mechanism in the evolution of star clusters. We describe early results of an extensive program in which an approximate theoretical treatment of such encounters is compared statistically with the results of numerous accurate numerical calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01230174
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