Constraint on Hybrid Stars with Gravitational Wave Events

Kilar Zhang,Feng-Li Lin

doi:10.3390/universe6120231

Abstract

Motivated by the recent discoveries of compact objects from LIGO/Virgo observations, we study the possibility of identifying some of these objects as compact stars made of dark matter called dark stars, or the mix of dark and nuclear matters called hybrid stars. In particular, in GW190814, a new compact object with 2.6 M⊙ is reported. This could be the lightest black hole, the heaviest neutron star, and a dark or hybrid star. In this work, we extend the discussion on the interpretations of the recent LIGO/Virgo events as hybrid stars made of various self-interacting dark matter (SIDM) in the isotropic limit. We pay particular attention to the saddle instability of the hybrid stars which will constrain the possible SIDM models.

Highlights

The LIGO/Virgo events GW170817 [1,2] and GW190425 [3] are in general considered as binaries of neutron stars (BNSs), as well as the possibility of being binaries of hybrid stars
We consider the dark stars and hybrid stars of all three scenarios based on the equations of state (EoSs) extracted from the bosonic self-interacting dark matter (SIDM) models discussed in Section 2 in the isotropic limit
We have extended the usual study of dark and hybrid stars for φ4 SIDM to more general types of bosonic SIDM models by extracting their EoSs in the isotropic limit so that we can have more access to the complete mass–radius relations for the TOV configurations

Summary

Introduction

The LIGO/Virgo events GW170817 [1,2] and GW190425 [3] are in general considered as binaries of neutron stars (BNSs), as well as the possibility of being binaries of hybrid stars. There are possibilities for this compact object to be a hybrid star made of neutron and dark matter [5]. In light of the varieties of dark matter models, it is easy for the resultant dark stars to cover a wide mass range, say 1 to 5 M , or even one order higher with proper parameters This makes the dark stars or the hybrid stars of dark and nuclear matters to be highly possible candidates to explain the companion star of GW190814. It is known that the TLN of black holes in Einstein gravity is vanishing, and the overall TLN effect for a compact binary coalescence event is a weighted average of the individual TLNs. for GW190814, the overall tidal effect is insignificant in the resultant gravitational waveform due to the high mass ratio between black hole and the companion star.

EoS for Bosonic SIDM in the Isotropic Limit

BTM Criteria and Saddle Instability for Hybrid Stars

Dark Star and and Hybrid Star Interpretations

Conclusions