1990 Fiscal Year Final Research Report Summary
The Theoretical Study on the Non-1inear Growing Process of Perturbations in the Astrophysical Systems including the Shear Flow.
| Project/Area Number |
01540220
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Astronomy
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| Research Institution | National Astronomical Observatory |
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Principal Investigator |
MIYAMA Shoken National Astron. Obs., Division of Theoretical Astrophysics, Associate Prof., 理論天文学研究系, 助教授 (00166191)
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| Co-Investigator(Kenkyū-buntansha) |
SEKIYA Minoru Teikyo University, Faculty of Science and Technology, Lecturer, 理工学部, 講師 (60202420)
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| Project Period (FY) |
1989 – 1990
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| Keywords | Differentially Rotating System / Shear Instability / Non-Linear Process / Accretion Disk / Weak Non-Linear Theory |
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| Research Abstract |
In astrophysical Phenomena, shear flows often exist, i. e., the flow in which there is the velocity gradient along the flow direction. Such flows are found in accretion disks around neutron stars and black holes and in the boundary region between ambient matters and jets from radio galaxies as well as bipolar flows from proto-stars. In hydrodynamics, the shear flows are well-known to be unstable and systems including them become turbulent states. But in astrophysics, the growth process of the unstable perturbations has been not understood yet. Hence the purpose of this proposed study is investigations about the non-linear growth process of the unstable modes which come from the existence of the shear flow.
As for the prototype model including the shear flow, we concentrate out study on differentially rotating disks. In order to analyze the non-linear process we use a weak non-linear theory, which is useful approximation method and applicable near the critical point where the growth rate of the linear perturbation is very small. Using this theory, because we can investigate analytically, it is very useful.
Since this study is the first attempt to analyze the shear instability in the differentially rotating disks, we take one of the simplest model, i. e., an incompressible cylinder which distribution of specific angular momentum is uniform. As the results we find that the non-linearity suppresses the linear growth and there is a new quasi-stationary state. And we find that the system oscillates with finite amplitudes around that state. These results agree with the numerical results as obtained so far. We consider that non-linear oscillations are very interesting for the mechanism of the angular transfer because they are nonーaxisymmetric waves.
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