Universal relations for differentially rotating relativistic stars at the threshold to collapse

Understand

A binary neutron star merger produces a rapidly and differentially rotating compact remnant whose lifespan heavily affects the electromagnetic and gravitational emissions.

• Its stability depends on both the equation of state (EOS) and the rotation law and it is usually investigated through numerical simulations.
• Nevertheless, by means of a sufficient criterion for secular instability, equilibrium sequences can be used as a computationally inexpensive way to estimate the onset of dynamical instability, which, in general, is close to the secular one.
• This method works well for uniform rotation and relies on the location of turning points: stellar models that are stationary points in a sequence of equilibrium solutions with constant rest mass or angular momentum.