Project/Area Number  01540220 
Research Category 
GrantinAid for Scientific Research (C).

Research Field 
Astronomy

Research Institution  National Astronomical Observatory 
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)

CoInvestigator(Kenkyūbuntansha) 
SEKIYA Minoru Teikyo University, Faculty of Science and Technology, Lecturer, 理工学部, 講師 (60202420)

Project Fiscal Year 
1989 – 1990

Project Status 
Completed(Fiscal Year 1990)

Budget Amount *help 
¥1,400,000 (Direct Cost : ¥1,400,000)
Fiscal Year 1990 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1989 : ¥1,000,000 (Direct Cost : ¥1,000,000)

Keywords  Differentially Rotating System / Shear Instability / NonLinear Process / Accretion Disk / Weak NonLinear Theory / 差動回転系 / シア不安定性 / 非線型現象 / アクリションディスク / 弱非線型理論 / シアス安定性 / 流体シミュレション 
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 protostars. In hydrodynamics, the shear flows are wellknown 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 nonlinear 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 nonlinear process we use a weak nonlinear 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 nonlinearity suppresses the linear growth and there is a new quasistationary 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 nonlinear oscillations are very interesting for the mechanism of the angular transfer because they are nonーaxisymmetric waves.
