Oscillation modes of hybrid stars within the relativistic Cowling approximation

Abstract

The first direct detection of gravitational waves has opened a new window to study the Universe and would probably start a new era: the gravitational wave Astronomy. Gravitational waves emitted by compact objects like neutron stars could provide significant information about their structure, composition and evolution.In this paper we calculate, using the relativistic Cowling approximation, the oscillations of compact stars focusing on hybrid stars, with and without a mixed phase in their cores. We study the existence of a possible hadron-quark phase transition in the central regions of neutron stars and the changes it produces on the gravitational modes frequencies emitted by these stars. We pay particular attention to the g-modes, which are extremely important as they could signal the existence of pure quark matter inside neutron stars. Our results show a relationship between the frequency of the g-modes and the constant speed of sound parametrization for the quark matter phase. We also show that the inclusion of color superconductivity produces an increase on the oscillation frequencies.We propose that observations of g-modes with frequencies f g between 1 kHz and 1.5 kHz should be interpreted as an evidence of a sharp hadron-quark phase transition in the core of a compact object.

Magnetized hybrid stars: effects of slow and rapid phase transitions at the quark–hadron interface

“…The hybrid magnetised EoS was obtained by combining the GM1L parametrisation of the RMF model for the hadron phase and the FCM model for the quark phase. Although it has been already shown that the hybrid EoS GM1L+FCM without MF satisfies the observational mass constraint of 2M (see, for example,Ranea-Sandoval et al (2018); Orsaria et al(2019)), we have extended the study of hybrid stars considering the effect of the MF on the EoS describing their matter composition. Our results show that both the 2M limit and the tidal deformability constraint are verified both when magnetized GM1L hadronic EoS or magnetised GM1L+FCM hybrid EoS are used.…”

Phase transitions in neutron stars and their links to gravitational waves

“…a full pasta phase calculation, must be used taking into account the formation of phase structures in the mixed phase [138]. Recently, several works have included finite-size effects at the hadron-quark phase transition in a phenomenological way, mimicking the mixed phase by a function which depends on the broadening of the phase transition [30,131,139]. Therefore, the Gibbs construction for the mixed phase can be simulated through a continuous interpolation between the hadronic and quark phases to mimic the mixing or percolation [30].…”

“…Moreover, as shown in Refs. [30,[250][251][252][253] the g-mode frequency strongly depends on the amplitude of the discontinuity, as it is shown in figure 9. Thus, it could be used to infer the value of the density jump and shed some light on the properties of the hadron-quark transition.…”

“…(Color online) Universal relationship between the g-mode frequencies and the ∆ / trans parameter of the CSS parametrization for quark matter, obtained for different EoSs. Figure adapted from Ref [30]…”

Effects of Hadron-Quark Phase Transitions in Hybrid Stars within the NJL Model

“…The universal relationship proposed in Ref. [30] between x CSS ≡ ∆ / trans , one of parameters of the Constant Speed of Sound (CSS) parametrization for quark matter [53,77], and the frequency of the g-modes. The original fitting function is y old fit = c old 1 log(x CSS ) + c old 2 with c old 1 = 0.454 ± 0.031 and c old 2 = 0.235 ± 0.023.…”