Tidal heating in binary inspiral of strange quark stars

TL;DR

This work investigates tidal heating in binary inspirals of strange quark stars arising from bulk viscosity of unpaired strange quark matter described by a non-ideal bag model. By modeling the f-mode–tidal coupling and the temperature evolution during inspiral, it predicts a gravitational-wave phase shift of order 0.1–0.5 radians for strange-quark mass around 200 MeV in equal-mass binaries with masses between 1.4 and 1.8 solar masses, potentially detectable by next-generation detectors. The analysis indicates that hyperon bulk viscosity would dominate only for very massive systems, so a detectable signal in lower-mass binaries would favor the strange quark star scenario. These results motivate incorporating tidal-dissipation effects into GW waveform models and exploring other quark matter phases in the context of binary inspirals.

Abstract

We investigate tidal heating associated with the binary inspiral of strange quark stars and its impact on the resulting gravitational wave signal. Tidal heating during the merger of neutron stars composed of nuclear matter may be considered negligible, but it has been demonstrated recently that the presence of hyperons at high densities could significantly enhance the dissipation during inspiral. In this work, we evaluate the bulk viscosity arising from non-leptonic weak processes involving quarks and show that it can be several orders of magnitude higher than the viscosity of nuclear matter at temperatures relevant to the inspiral phase of the merger of strange stars. We model strange quark matter in the normal phase using a non-ideal bag model including electrons and ensure compatibility with astrophysical constraints. By analysing equal-mass binary systems with component masses ranging from 1.4 to 1.8 $\, M_{\odot}$, we find that temperatures close to 0.1 MeV are reached by the end of the inspiral phase. We also estimate the effect on the gravitational waveform and conclude that the additional phase shift could range from $0.1$ to $0.5$ radians for strange quark masses of 200 MeV, making it potentially detectable by next-generation gravitational wave detectors. Given that tidal heating from hyperons is dominant only for very massive neutron stars having masses 1.8 to 2.0 $\, M_{\odot}$, a successful detection of this phase shift during the inspiral of binary systems with relatively low masses of 1.4 to 1.6 $\, M_{\odot}$ could be a smoking gun signature for the existence of strange quark stars.

Figures (6)

• Figure 1: Stability window for the non-ideal bag model. The strange quark mass $m_s$ is plotted as a function of $B_{\rm eff}^{1/4}$ for three different values of the nonperturbative parameter $a_4$. The shadow regions represent stable strange quark matter according to the Bodmer-Witten conjecture. We have imposed $m_s=95$ MeV as the lowest value of the strange quark mass ParticleDataGroup:2024cfk.
• Figure 2: M-R sequences for the EoS parametrization tabulated in \ref{['tab:EoSs']}. Horizontal bands correspond to masses $M=2.08{\pm 0.07} M_{\odot}$ of PSR J0740$+$6620 Fonseca2021 and $M=2.01^{+0.04}_{-0.04} M_{\odot}$ of PSR J0348$+$0432 Antoniadis2013. The 90% contour of M-R measurement for PSR J0740+6620 corresponding to Riley et al. Riley2021J0740_new is shown in black, and for PSR J0030+0451 Riley_2019J0030_new is shown in magenta. The M-R estimate of the lightest compact object HESS J1731-347 Hess is shown by the shaded area labelled with 'HESS J1731-347'. Although recent works Hess_reanalysis puts the original spectral analysis into question. The M-R estimates of the two companion stars of the merger event GW170817 are shown by the shaded area labelled with GW170817 M1 (M2).
• Figure 3: Relative strengths of various sources of viscosities of dense matter inside neutron stars as a function of temperature at $n_B=2.5n_0$ with $n_0\approx 0.15$ fm$^{-3}$. The bulk viscosity at $\omega= 2\pi$ kHz before and after the resonant peak is shown for the strange-quark-matter EoSs (Set A-F) detailed in \ref{['tab:EoSs']}, non-leptonic reactions involving $\Lambda$ hyperons, and m-Urca processes in nuclear matter. We also plot, the standard neutron matter shear viscosity coming from $ee$ scattering $\eta_{SV}^{e}$, and the shear viscosity in degenerate quark matter coming from quark-quark scattering $\eta_{SV}^{qq}$.
• Figure 4: Estimates of the average final temperature due to the tidal dissipation as a function of GW frequency for the six different EoSs (Sets A-F) considered for three different equal mass binary systems: a) $1.4M_{\odot}$ (top panel) b) $1.6M_{\odot}$ (mid panel) and c) $1.8M_{\odot}$ (bottom panel).
• Figure 5: The cumulative phase due to the tidal dissipation as a function of GW frequency for the sets of EoSs and three different equal mass binary systems: a) $1.4M_{\odot}$ (top panel) b) $1.6M_{\odot}$ (mid panel) and c) $1.8M_{\odot}$ (bottom panel). The phase uncertainty limits for next generation detectors : A+ Aplus_sensitivity, 40-km Cosmic Explorer(CE) CECE2 and Einstein Telescope(ET) Hild_2011 are also plotted in solid lines for a source at $100$ Mpc.