Some time ago, using three different 3D hydrodynamic simulation tools, Durisen et al. (1986) followed the development to nonlinear amplitudes of a two-armed, spiral-mode instability that arises naturally in rapidly rotating, self-gravitating systems. The particular initial model that was examined had an n = 3/2 polytropic equation of state, an n' = 0 angular momentum distribution, and an initial ratio of rotational to gravitational potential energy T/|W| = 0.33. The simulation tools that were used at the time were relatively crude, compared to tools that are available today.
For comparison, we also have studied the development of the same type of two-armed (bar-mode), spiral instability in a model having an n = 3/2 polytropic equation of state and an initial T/|W| = 0.28, but with an angular momentum distribution specified to produce a uniform vortensity profile in the initial model, where vortensity is defined to be the ratio of vorticity to mass density (Cazes 1999, Cazes & Tohline 1999). The movie labeled here as Model B shows this evolution from an inertial reference frame and covers approximately 32 dynamical times as defined by the mean density of the initial model. The instability in this model has less of a pronounced spiral character, but ultimately results in the formation of a new triaxial equilibrium configuration with properties that are similar to the end-state of the Model A evolution.
As illustrated and discussed elsewhere we are convinced that the dynamically stable triaxial configurations that have been formed through both of these model simulations are compressible analogs of Riemann S-type ellipsoids. As such, they can provide important clues to our understanding of the evolution of protostellar gas clouds and the possible fission of such clouds into binary star systems; long-lived gaseous bars in galaxies; and compact stellar structures that may appear as continuous sources of gravitational radiation.
|Producer||Visualization Directors||Scientific Director|
|Joel E. Tohline||
John E. Cazes
Howard S. Cohl
John E. Cazes
This work has been supported, in part, by the U.S. National Science Foundation through grant AST-9528424 and, in part, by grants of high-performance-computing time at the San Diego Supercomputer Center and through the PET program of the NAVOCEANO DoD Major Shared Resource Center in Stennis, MS.