Classical Idea (based on incompressible fluids)

A slowly rotating core region in a Giant Molecular Cloud undergoes a dynamic gravitational collapse. As it collapses, it remains axisymmetric and so spins-up and flattens out (becomes oblate). Eventually the density of the increases increases to the point where the optical depth becomes greater than 1 and the heat generated by the collapse may be trapped in the collapsing core. At this point the dynamical collapse slows and the core quasi-statically contracts; its evolution driven by the slow increase of its mass and angular momentum due to accretion and cooling. As the core region contracts, it spins-up and may reach the bar mode stability limit. If the bar mode becomes unstable, the core will be driven to a bar-like configuration.

The next lowest order nonaxisymmetric mode deforms the oblate spheroid into ta bar (via the bar mode). As the bar continues to accrete and cool, it spins-up and becomes unstable to the next lowest order mode, the pear mode. The figure then continues to evolve becoming unstable to successively higher and higher order modes until the center pinches-off leaving a binary star system. The basic classical idea did not work because the nature of the instabilities changed for the higher order modes. However, the notion of fission persisted.

WATER DROPLETS

Ref: Wang, Taylor

A slowly rotating water droplet in a weightless environment (Shuttle experiment) provides a nice example of fission in a rotating incompressible fluid.