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  • 1
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    The effect of rotation on the hydrodynamics of stellar collapse (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Keywords: ASTROPHYSICS
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  • 2
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    Collapse and equilibrium of rotating, adiabatic clouds (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A numerical hydrodynamics computer code analysis of the collapse and establishment of equilibrium of adiabatic gas clouds restricted to axial symmetry found that the clouds are originally uniform in density and rotation. The method can compare the dynamic collapse and approach to equilibrium with the data on incompressible uniformly rotating equilibrium clouds and on equilibrium structures of differentially rotating polytropes. It is concluded that the stellar formation theory indicates that the low alpha fragments produced at the termination of the dynamic isothermal collapse phase of interstellar clouds may undergo significant dynamic collapse in an adiabatic regime leading to transitory ring formation and additional fragmentation on a smaller scale.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 242
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  • 3
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    A heuristic criterion for instability to fragmentation in rotating, interstellar clouds (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A heuristic criterion, based on linear perturbation analysis, is applied to the initial growth of density perturbations in isothermal or adiabatic gas clouds, with initially uniform density and uniform rotation. The heuristic criterion is shown to be consistent with the available results from numerical calculations of cloud collapse. The criterion predicts that perturbations varying as cos(m-phi) will be most likely to grow when m is small, unless the cloud is nearly pressureless.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 259
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  • 4
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    Collapse of accreting, rotating, isothermal, interstellar clouds (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The evolutions of the envelopes of collapsing, accreting, isothermal clouds have been numerically calculated for both spherically symmetric and rotating (axisymmetric) clouds. The results provide a cohesive picture of isothermal collapse, and their relationship to previous numerical calculations and similarity solutions is discussed. Even with a large initial rotation rate, the majority of the cloud envelope is accreted, in one case leaving behind a large-scale circulation current. The calculations are performed for both initially uniform density and centrally condensed clouds. Density and velocity profiles for a wide variety of observed systems are compared with those obtained in this study, providing a preliminary assessment of the stage of evolution and initial structure for the observed systems.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 258
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  • 5
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    Collapse and fragmentation of rotating, adiabatic clouds (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A numerical hydrodynamics code has been used to calculate the collapse of rotating, adiabatic clouds. The three-dimensional nature of the calculation allows the clouds to fragment in the dynamic collapse phase. Clouds with adiabatic exponent of 7/5 and initial cos(2 phi) density variations fragment into binary systems if the initial ratio of thermal to gravitational energy is small (about 0.05). Clouds with higher thermal energy, however, damp the density variation and form near-equilibrium ellipsoids, with ratios of rotational to gravitational energy less than the critical value for dynamic growth of nonaxisymmetry in Maclaurin spheroids. Even with an adiabatic pressure law, dynamic fragmentation of a collapsing cloud is possible, implying for star formation theory that the low thermal energy fragments produced in isothermal collapse calculations may undergo a subsequent dynamic fragmentation in the nonisothermal regime.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 250
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  • 6
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    Collapse, equilibrium, and fragmentation of rotating, adiabatic clouds (1980)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Numerical calculations of the collapse of adiabatic clouds from uniform density and rotation initial conditions show that when restricted to axisymmetry, the clouds form either near-equilibrium spheroids or rings. Rings form in the collapse of low thermal energy clouds and have a ratio of rotational kinetic energy to the absolute value of gravitational potential energy greater than approximately 0.43. When the axisymmetric constraint is removed and an initial m = 2 density variation is introduced, clouds either collapse to form near-equilibrium ellipsoids or else fragment into binary systems through a bar phase. Ellipsoids form in the collapse of high thermal energy clouds and have a rotational kinetic energy/absolute value of gravitational potential energy ratio less than approximately 0.27. The results are consistent with the critical values of the rotational kinetic energy/absolute value of gravitational potential energy ratio for instabilities in Maclaurin spheroids, and suggest that protostellar clouds may undergo a dynamic fragmentation in the nonisothermal collapse regime.
    Keywords: ASTROPHYSICS
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  • 7
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    Fragmentation of a nonisothermal protostellar cloud (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The collapse of a very low thermal energy, rotating cloud results in fragmentation to a binary protostellar system even in the nonisothermal regime. The solar system therefore probably did not form from a fragmentation hierarchy involving ejection of the presolar nebula from a multiple system.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 55; July 198
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  • 8
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    Numerical three dimensional calculations of tidally induced binary protostar formation (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The manner in which interstellar clouds fragment into subcondensations capable of becoming stars is still unknown. A variety of mechanisms may be responsible for cloud fragmentation. The considered investigation is concerned with a mechanism which is based on tidal forces due to a companion cloud. A 3D code is used to study the tidal effects of point sources of various masses located in the equatorial plane of an initially uniform density, uniformly rotating, isothermal gas cloud. It is found that tidal forces can be quite effective at inducing fragmentation in an initially uniform cloud, although the effects are most pronounced for low thermal energy clouds, perturbed by perhaps unreasonably large tidal forces. It is also seen that tidal forces may be much less efficient at preventing the collapse of a cloud than has previously been supposed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 246
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  • 9
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    Dynamical constraints on the origin of the moon (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Six different categories of models for the formation of the moon within the context of the general theory of terrestial planet formation by the accumulation of protoplanets are discussed. These catagories are: (1) rotational fission; (2) precipitation fission; (3) intact capture; (4) disintegrative capture; (5) binary accretion; and (6) giant impact accretion. It appears that the only plausable mechanism proposed thus far involves the formation of the Moon following a giant impact that ejects portions of the differentiated Earth's mantle and parts of the impacting body into circumterrestrial orbit.
    Keywords: ASTROPHYSICS
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 115
    Format: application/pdf
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  • 10
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    On the fragmentation of rotating interstellar clouds (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Simple physical arguments are used to estimate the time scale for fragmentation of a collapsing, rotating, isothermal, interstellar cloud. This time scale is compared with a similarly estimated time scale for the collapse upon itself of a transitory ring structure. It is shown to be plausible for a cloud with a given ratio of rotational to gravitational energy (beta) that as the ratio of thermal to gravitational energy (alpha) is varied, there is an intermediate range of alpha where a ring forms and collapses on itself, prior to fragmentation. For higher or lower alpha, however, the cloud fragments prior to ring self-collapse. The analysis is compared with the results of numerical multidimensional, gravitational, hydrodynamical collapse and shown to be in good agreement with them.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 244
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