• asteroseismology;
  • equation of state;
  • gravitational waves;
  • methods: numerical;
  • stars: neutron;
  • stars: oscillation


We study the excitation of non-axisymmetric modes in the post-merger phase of binary compact object mergers and the associated gravitational wave emission. Our analysis is based on general-relativistic simulations, in the spatial conformal flatness approximation, using smoothed particle hydrodynamics for the evolution of matter, and we use a set of equal- and unequal-mass models, described by two non-zero-temperature hadronic equations of state and by one strange star equation of state. Through Fourier transforms of the evolution of matter variables, we can identify a number of oscillation modes, as well as several non-linear components (combination frequencies). We focus on the dominant m= 2 mode, which forms a triplet with two non-linear components that are the result of coupling to the quasi-radial mode. A corresponding triplet of frequencies is identified in the gravitational wave spectrum, when the individual masses of the compact objects are in the most likely range of 1.2–1.35 M. We can thus associate, through direct analysis of the dynamics of the fluid, a specific frequency peak in the gravitational wave spectrum with the non-linear component resulting from the difference between the m= 2 mode and the quasi-radial mode. Once such observation becomes available, both the m= 2 and quasi-radial mode frequencies could be extracted, allowing for the application of gravitational wave asteroseismology to the post-merger remnant and leading to tight constraints on the equation of state of high-density matter.