Viscosity and magnetic fields drive differentially rotating stars toward uniform rotation, and this process has important consequences in many astrophysical contexts. For example, merging binary neutron stars can form a “hypermassive” remnant, i.e. a differentially rotating star with a mass greater than would be possible for a uniformly rotating star. The removal of the centrifugal support prov...

We present two-dimensional numerical simulations of gravitational collapse of a rotating cloud. The collaping cloud forms a dynamically contracting disk. The disk structure can be well reproduced by a similarity solution. The similarity solution has only two parameters, the sound speed (cs) and the ratio of the speci c angular momentum to the mass (!). The disk mass is independent of the mass o...

Purely gravitational perturbations are considered in a thin rotating disk composed of several gas and stellar components. The dispersion relation for the axisymmetric density waves propagating through the disk is found and the criterion for the local axisymmetric stability of the whole system is formulated. In the appropriate limit of two-component gas we confirm the findings of Jog & Solomon (...