When two neutron stars merge, the remnant can survive briefly as a rapidly rotating hyper-massive neutron star before collapsing into a black hole. How long it survives and what it looks like encodes information about the equation of state at densities far beyond anything accessible in a terrestrial experiment.

This paper constructs quasi-stationary equilibrium sequences of hyper-massive neutron stars using exotic equations of state that include strange quark matter, hyperons, and other non-nucleonic degrees of freedom. We map out how the remnant mass, angular momentum, and oscillation frequencies change with the underlying microphysics, giving a theoretical foundation for interpreting post-merger gravitational wave signals from next-generation detectors.

Published in Journal of Astrophysics and Astronomy (2022)