Gravitational wave asteroseismology limits from low density nuclear matter and perturbative QCD

Abstract

We investigate the fundamental mode of non-radial oscillations of non-rotating compact stars in general relativity using a set of equations of state (EOS) connecting stateof-the-art calculations at low and high densities. Specifically, a low density model based on the chiral effective field theory (EFT) and high density results based on perturbative Quantum Chromodynamics (QCD) are matched through different interpolating polytropes fulfilling thermodynamic stability and subluminality of the speed of sound, together with the additional requirement that the equations of state support a two solar mass star. We employ three representative models (EOS I, II and III) presented in Ref.[1] such that EOS I gives the minimum stellar radius, EOS II the maximum stellar mass, and EOS III the maximum stellar radius. Using this family of equations of state, we find that the frequency and the damping time of the f -mode are constrained within narrow quite model-independent windows. We also analyze some proposed empirical relations that describe the f -mode properties in terms of the average density and the compactness of the neutron star. We discuss the stringency of these constrains and the possible role of physical effects that cannot be encoded in a mere interpolation between low and high density EOSs.

Gravitational wave signatures of highly magnetized neutron stars

“…On the other hand, it is clear that the constitution of the star plays a very important role and the frequency generated by massive hyperonic stars (larger than 1.8 M ) is greatly increased as compared with their nucleonic counterparts. It is also observed that the gravitational wave frequencies of the fundamental modes for our models fall in the range of 1.4 and 2 kHz for stars with masses between 1.4 and 2.4 M ; these values correspond with previous results in the literature [92,93] obtained with less realistic EOS. We can see that in general a high magnetic field produces little effect on the frequency window.…”

Constraining Dense Matter Physics Using f-Mode Oscillations in Neutron Stars

“…It is interesting here to compare the above results (obtained within the Cowling approximation and the RMF model framework) with those presented in Ref. [20] (see e.g., the left panel of Figure 3 in Ref. [20]), which were obtained from quite model-independent EoS limits based on low-density nuclear matter and perturbative QCD, using the full linearized oscillation equations.…”

“…Fits using such EoSs have been used to derive relations between mode frequencies and global variables (mean density, compactness). Recently, in [20], the frequency and the damping time of f -modes have been constrained within narrow windows using quite model-independent EOSs derived from the nuclear matter at low densities and perturbative quantum chromodynamcs (QCD) at high densities, connected by interpolating subluminal monotropes at intermediate densities. Although the dispersion of frequencies due to different EoSs in such studies is evident, one cannot compare between the chosen EoSs as they correspond to very different nuclear matter properties.…”

Phase transitions in neutron stars and their links to gravitational waves

“…These results suggest that the mass and radius of a compact object could be inferred if f and τ were detected by the new generation of gravitational wave detectors. In a recent work, the properties of the fundamental mode have been systematically studied using a set of EoS connecting state-of-the-art calculations at low and high densities [238]. Specifically, a low density model based on the chiral effective field theory (EFT) and high density results based on perturbative Quantum Chromodynamics (QCD) are matched through different interpolating polytropes fulfilling thermodynamic stability and subluminality of the speed of sound, together with the additional requirement that the equations of state support a two solar mass NS.…”