On the Dynamical Stability of Uber-massive Neutron Stars

The joint detection of gravitational wave (GW) and electromagnetic (EM) signals resulting from the merger of two neutron stars (NS) was a breakthrough in multi-messenger astronomy. A possible remnant of NS-NS mergers is a hyper-massive neutron star (HMNS): a transient configuration that is supported from gravitational collapse by additional centrifugal support due to differential rotation. The space of differentially rotating stars is rich, exhibiting different types of solutions among which there exist configurations that can support more than 2 times the maximum mass of a TOV star. We call these configurations uber-massive. The dynamical stability of uber-massive neutron stars (UMNS) and of the different types of HMNSs has not been studied, yet. We present results from dynamical simulations in general relativity addressing this issue. The primary focus is on UMNSs with the largest possible rest mass and on different types of HMNSs with smaller rest mass. A diverse set of outcomes is explored including gravitational collapse, long lifetimes, and migration to dynamically stable configurations.