Hybrid stars with sequential phase transitions: the emergence of the g2 mode

M.C Rodríguez,O.M Guilera,M G Orsaria,G Malfatti,Ignacio F Ranea-Sandoval,M Mariani

doi:10.1088/1475-7516/2021/02/009

Abstract

Neutron stars are the densest objects in the Universe, with M ∼ 1.4 M⊙ and R ∼ 12 km, and the equation of state associated to their internal composition is still unknown. The extreme conditions to which matter is subjected inside neutron stars could lead to a phase transition in their inner cores, giving rise to a hybrid compact object. The observation of 2M⊙ binary pulsars (PSR J1614-2230, PSR J0343+0432 and PSR J0740+6620) strongly constraints theoretical models of the equation of state. Moreover, the detection of gravitational waves emitted during the binary neutron star merger, GW170817, and its electromagnetic counterpart, GRB170817A, impose additional constraints on the tidal deformability. In this work, we investigate hybrid stars with sequential phase transitions hadron-quark-quark in their cores.{We assume that both phase transitions are sharp and analyse the rapid and slow phase conversion scenarios.} For the outer core, we use modern hadronic equations of state. For the inner core we employ the constant speed of sound parametrization for quark matter. We analyze more than 3000 hybrid equations of state, taking into account the recent observational constraints from neutron stars. The effects of hadron-quark-quark phase transitions on the normal oscillation modes f and g, are studied under the Cowling relativistic approximation. Our results show that, in the slow conversion regime, a second quark-quark phase transition gives rise to a new g2 mode. We discuss the observational implications of our results associated to the gravitational waves detection and the possibility of detecting hints of sequential phase transitions and the associated g2 mode.

Highlights

IntroductionParametrization for quark matter (see, for example, Refs. [6, 13]). One of their main conclusions is that twin configurations (i.e stable stellar configurations with a given mass but different radius, for more details see section 3.1) can be obtained, and triplets
The first direct detection of gravitational waves (GW) coming from the merger of NSs, GW170817, [21] and its electromagnetic counterpart [22] help to restrict the EoS of dense matter putting constraints on the radius of a 1.4M NS [23, 24]
Combining this information with other astronomical observations, recently it has been suggested that quark matter should be present in the inner cores of very massive NSs [25]

Summary

Introduction

Parametrization for quark matter (see, for example, Refs. [6, 13]). One of their main conclusions is that twin configurations (i.e stable stellar configurations with a given mass but different radius, for more details see section 3.1) can be obtained, and triplets. The first direct detection of GW coming from the merger of NSs, GW170817, [21] and its electromagnetic counterpart [22] help to restrict the EoS of dense matter putting constraints on the radius of a 1.4M NS [23, 24]. Combining this information with other astronomical observations, recently it has been suggested that quark matter should be present in the inner cores of very massive NSs [25]. This assumption allows us to study different families of stable configurations and to generalize the analysis about the possible existence (or not) of twin

Objectives

Results

Conclusion