Oscillation modes and gravitational waves from strangeon stars

The strong interaction at low-energy scales determines the equation of state (EOS) of supranuclear matters in neutron stars (NSs). It is conjectured that the bulk dense matter may be composed of strangeons, which are quark clusters with nearly equal numbers of u, d, and s quarks. To characterize the strong-repulsive interaction at short distance and the non-relativistic nature of strangeons, a phenomenological Lennard-Jones model with two parameters is used to describe the EOS of strangeon stars (SSs). For the first time, we investigate the oscillation modes of non-rotating SSs and obtain their frequencies for various parametrizations of the EOS. We find that the properties of radial oscillations of SSs are different from those of NSs, especially for stars with relatively low central energy densities. Moreover, we calculate the f-mode frequency of non-radial oscillations of SSs within the relativistic Cowling approximation. The frequencies of the f mode of SSs are found to be in the range 6.7-8.7 kHz. Finally, we study the universal relations between the f-mode frequency and global properties of SSs, such as the compactness and the tidal deformability. The results we obtained are relevant to pulsar timing and gravitational waves, and will help to probe NSs' EOSs and infer non-perturbative behaviours in quantum chromodynamics.