GW170817 and GW190425 as hybrid stars of dark and nuclear matter

Abstract

We propose three scenarios for compact hybrid stars composed of nuclear and dark matter. These hybrid stars could provide alternative interpretations to the LIGO/Virgo events GW170817 and GW190425. To demonstrate our proposal, we solve the Tolman–Oppenheimer–Volkoff configurations of hybrid stars by using the SLy4, APR4, and SKb equations of state (EoS) for nuclear matter, and an EoS for a bosonic self interacting dark matter (SIDM) proposed by Colpi et al. (Phys Rev Lett 57:2485, 1986). We then obtain their mass–radius and tidal Love number (TLN)-mass relations, and further examine the possible saddle instability of these compact objects by the generalized Bardeen–Thorne–Meltzer (BTM) criteria. Our results show that the hybrid star scenarios are able to explain GW170817 and GW190425. Some hybrid stars can have compact neutron or mixed cores around 10 km while possessing thick dark matter shells, thus they can be more massive than the maximum mass of the typical neutron stars but are electromagnetically detected with about the same size of neutron stars. Reversely, we also infer the dark matter model from the parameter estimation of GW190425. Our proposed hybrid stars can be further tested by the coming LIGO/Virgo O3 events.

Dark Stars and Gravitational Waves: Topical Review

“…Since dark matter almost does not interact with the baryonic ones, and we have little idea of the nature of dark matter, it is hard to pin down the internal structure of the hybrid stars. By simply classifying the geometric setup, we can have three types of hybrid stars [116,117]. The first type (called Scenario I) is to have a neutron core covered by a dark matter shell, and the second type (called Scenario II) is to have a dark matter core covered by a neutron shell.…”

“…Of course, this will add up the variety of compact stars and cause more difficulty when identifying the sources of the gravitational events. In [116,117], all three scenarios have been studied and adopted to fit some gravitational wave events. Below, we will review some essential ingredients of hybrid stars in [116,117].…”

“…In [116,117], all three scenarios have been studied and adopted to fit some gravitational wave events. Below, we will review some essential ingredients of hybrid stars in [116,117].…”

Tidal Deformability of Dark Matter Admixed Neutron Stars

“…From the analogy to the Newtonian situation, we can construct a set of equations by considering the pressure of one component will not support the other component. We have a two-fluid version of the TOV equation [37,47]:…”

“…Compact objects with DM admixture have been studied previously, such as supernova progenitors [35,36] and neutron stars (see, e.g., [37][38][39][40][41][42][43][44][45][46][47][48][49]).…”