For Kerr black holes, the spinning rates can be described by a normalized spin parameter $a=cJ/GM^2$, which takes any values between 0 and 1 regardless of the masses of the black holes. If we use the same parameter to describe neutron stars, what’s the maximum a neutron stars can achieve (without being destabilized)? Is this value invariant regardless of neutron star masses?
I asked this question because I have read several papers published by LIGO. Although LIGO detected several neutron star merger events, they can’t rule out the possibility black hole mergers of the same masses (if the neutron stars are too massive, they will collapse into a black hole directly with little EM signature). So I came up with an idea of using the spin parameter to tell the identity of mergers (because spin parameters are easy to determine). If the maximum spin parameter of neutron stars is higher or considerably lower than 1, we can easily rule out some possibilities.
