Abstract
Abstract The internal composition of neutron stars is currently largely unknown. Due to the possibility of phase transitions in quantum chromodynamics, stars could be hybrid and have quark cores. We investigate some imprints of elastic quark phases (only when perturbed) on the dynamical stability of hybrid stars. We show that they increase the dynamical stability window of hybrid stars in the sense that the onset of instabilities happens at larger central densities than the ones for maximum masses. In particular, when the shear modulus of a crystalline quark phase is taken at face value, the relative radius differences between elastic and perfect-fluid hybrid stars with null radial frequencies (onset of instability) would be up to 1%–2%. Roughly, this would imply a maximum relative radius dispersion (on top of the perfect-fluid predictions) of 2%–4% for stars in a given mass range exclusively due to the elasticity of the quark phase. In the more agnostic approach where the estimates for the quark shear modulus only suggest its possible order of magnitude (due to the many approximations taken in its calculation), the relative radius dispersion uniquely due to a quark phase elasticity might be as large as 5%–10%. Finally, we discuss possible implications of the above dispersion of radii for the constraint of the elasticity of a quark phase with electromagnetic missions such as NICER, eXTP, and ATHENA.
Highlights
Neutron stars (NSs) are very compact remnants of stellar evolution that offer ways to probe particle and dense-matter physics aspects not possible in terrestrial laboratories
Given that we are mainly interested in cold stars, we mostly focus our analysis on slow conversions
The points in the M(R) or M(ρc) relations where eigenfrequencies are null are not their critical points anymore. This is expected because the classical rules of dynamical stability of stars assume perfect fluids (Harrison et al 1965; Shapiro & Teukolsky 1986; Friedman et al 1988)
Summary
Neutron stars (NSs) are very compact remnants of stellar evolution that offer ways to probe particle and dense-matter physics aspects not possible in terrestrial laboratories. The observation of the GW170817 event, undoubtedly an inspiral of a binary NS system by the LIGOVirgo collaboration (Abbott et al 2017, 2018, 2019), has provided the first measurement of the late inspiral mutual tidal deformability of the components (in the form of the component mass-weighted sum of individual tidal deformabilities) This value, albeit burdened by large measurement errors, already constrains some microphysical models for the dense-matter equation of state (EOS) with and without phase transitions (see, e.g., Chatziioannou 2020; Morawski & Bejger 2020; Blacker et al 2020; Miao et al 2020; Ferreira et al 2020 and references therein). We work with geometric units, and our metric signature convention is (−, +, +, +)
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