Highly differentially rotatig neutron stars can be produced in core-collapse supernova explosions. These objects may be significantly more massive than rigidly rotating neutron staers. Even for a modest degree of differential rotation we find equilibrium solutions with masses up to 4 times larger then the TOV limit. While the rotation profile evolves into uniform rotation on secular timescales, the immediate fate of the hypermassive remnant may have impact on the gravitational wave and electromagnetic emission from core-collapse supernova.
We investigate the dynamical stability against radial and axisymmetric pertutbations of differentially rotating neutron stars. We use the 2D CoCoNuT code to perform a series of hydrodynamical simulations of hypermassive neutron stars. We check whether the object undergoes a prompt collapse or stays stable on dynamical timescales.
I will present our preliminary results of our stability studies for masses up to 2 times larger than TOV limit. The threshold to collapse that we find is close to the limit estimated by turning-point criterion.