Discontinuity gravity modes in hybrid stars: assessing the role of rapid and slow phase conversions

Abstract

Discontinuity gravity modes may arise in perturbed quark-hadron hybrid stars when a sharp density jump exists in the stellar interior and are a potential fingerprint to infer the existence of quark matter cores in compact objects. When a hybrid star is perturbed, conversion reactions may occur at the quark-hadron interface and may have a key role in global stellar properties such as the dynamic stability and the quasi-normal mode spectrum. In this work we study the role of the conversion rate at the interface. To this end, we first derive the junction conditions that hold at the sharp interface of a non-radially perturbed hybrid star in the case of slow and rapid conversions. Then, we analyse the discontinuity g-mode in both cases. For rapid conversions, the discontinuity g-mode has zero frequency because a displaced fluid element near the phase splitting surface adjusts almost immediately its composition to its surroundings and gravity cannot provide a buoyancy force. For slow conversions, a g-mode exists and its properties are analysed here using modern hadronic and quark equations of state. Moreover, it has been shown recently that in the case of slow conversions an extended branch of stable hybrid configurations arises for which ∂M/∂ǫc < 0. We show that g-modes of the standard branch (that is, the one with ∂M/∂ǫc > 0) have frequencies and damping times in agreement with previous results in the literature. However, g-modes of the extended branch have significantly larger frequencies (in the range 1 − 2 kHz) and much shorter damping times (few seconds in some cases). We discuss the detectability of g-mode GWs with present and planned GW observatories.

Neutron star equation of state: QMF modeling and applications

“…The possibility of the existence of strange quark matter in NS high-density cores is of special interest in the present era of GW astronomy [e.g., 9,101,164,165,166,167,168,169,170,171,172,173,174]. Presently, we have no unified models to address the hadron phase and the quark phase, and it is still not clear whether the change in the hadron phase corresponding to that in the quark phase is a crossover or a first-order transition.…”

Phase transition and stiffer core fluid in neutron stars: Effects on stellar configurations, dynamical stability, and tidal deformability

“…Through this diagnostic technique, analyzing the frequency modes can obtain a solid way to learn more about the physics inside compact stars. For example, if inside these stars a single component fluid is present [19][20][21][22][23][24][25][26][27][28][29][30][31][32] or the existence of a phase transition between layers with different mechanical properties [33][34][35][36][37][38][39][40][41][42][43][44][45][46].…”

“…In literature, unlike the study of one-phase static compact stars, two-phase stars and the impact of the phase transition on the properties of these stars were not widely investigated. There are studies analyzing how density jumps affect the static stellar equilibrium configuration and radial frequency of oscillations [34][35][36][37][38][39][40][41][42][43][44][45], as well as the possibility of arising of the so-called gravitational pulsation mode (gmode) [33][34][35].…”

“…As regards the radial perturbations of compact stars with a sharp interface, the set of equations must be solved by taking into account the additional boundary conditions at the phase-splitting interface. Around this point, there are two types of physical behavior due to radial perturbations: the slow and rapid phase conversion [35,36]. In the case of slow conversion, there is no change of matter over the pulsating interface.…”

Constraining hadron-quark phase transition parameters within the quark-mean-field model using multimessenger observations of neutron stars

“…The possible appearance of quark matter and deconfinement phase transition is one of unresolved puzzles of neutron star matter and could largely affect the underlying EOS. At present, since the quark matter EOS is poorly known at zero temperature and high density appropriate for neutron stars, one possible way of tackling the problem is to perform the calculations with certain quark matter models in sufficient large parameter space and then compare the predictions with observations of neutron star static and dynamical properties, which has been of special interest in the present era of gravitational wave astronomy (e.g., Burgio et al 2018;Nandi & Char 2018;Paschalidis et al 2018;Aloy et al 2019;Bauswein et al 2019;Christian et al 2019;Gomes et al 2019;Han & Steiner 2019;Montaña et al 2019;Most et al 2019;Orsaria et al 2019;Sieniawska et al 2019;Chatziioannou & Han 2020;Chen et al 2020;Essick et al 2020;Marczenko et al 2020;Nunna et al 2020;Pereira et al 2020;Tonetto & Lugones 2020;Weih et al 2020).…”