The third family of compact stars with the color-flavor locked quark core

Abstract

In this paper, we study the third family of compact stars with the color-flavor locked (CFL) quark core. The relativistic mean field model is used for hadronic matter and the MIT bag model for CFL quark matter. The results of the calculation show a transitional behavior that goes from the hadron star range, through the transition range, into the CFL quark star range. In the transition range, the third family of compact stars with the CFL quark matter core is found in the wide range of the CFL energy gap 100 MeV≤<150 MeV. By comparing with early investigations, we argue that the greatest possible third family of compact stars may be the hybrid stars with the CFL quark core. Neutron stars are natural laboratories to study the properties of compact matter [1,2]. In the interior of a neutron star there exist phase transitions from hadronic matter to various exotic matter, such as hyperonic matter, meson condensation and quark matter [3][4][5]. It is widely accepted that hadronic matter undergoes a phase transition to strange quark matter at the high density range [6,7]. The study of quantum chromodynamics (QCD) indicates that quark matter might be in a color superconducting phase at quite high density range [8,9]. The essence of color superconductivity is based on the Bardeen, Cooper, and Schrieffer (BCS) pairing mechanism [10]. Theoretical researchers generally agree that the ground state of QCD with three flavors is the color-flavor-locked (CFL) phase [11,12]. At present, the hybrid stars with a CFL quark matter core have been extensively studied [13][14][15]. Two families of compact stars, white dwarfs and neutron stars, are known well. Almost 40 years ago, Gerlach [16] found that a third family of stable configurations of compact stars could exist in nature besides two families of white dwarfs and neutron stars. He noted that it was due to a large discontinuous behavior in the speed of sound (dp/dε) of the corresponding equation of state (EoS). Glendenning [17] also found that the practical physical mechanism was a phase transition from hadronic to quark matter. Schertler et al. [18] investigated the phase transition from hadronic to normal quark matter and the possibility of the third family of compact stars. They concluded that the third family could serve as a signature for a phase transition from hadronic to quark matter. This paper will investigate the influence of the CFL energy gap on the bulk properties of neutron stars and discuss

From strangelets to strange stars: a unified description

“…Respectively, the SQM sphere contains 1.37×10 9 u-quarks, 1.48 × 10 9 d-quarks, 1.26 × 10 9 s-quarks, and 2.74 × 10 5 electrons, which gives the total core charge Q(R) = 2.66 × MeV. It is worth mentioning that if B exceeds the upper bound, SQM is unstable and may only exist at the core of a compact star, i.e., hybrid star [13,57].…”

“…We take the three typical values B 1/4 = 145, 152, and 159 MeV. It is worth mentioning that if B exceeds the upper bound, SQM is unstable and may only exist at the core of a compact star, i.e., hybrid star [13,57].…”

“…It was pointed out long ago that strange quark matter (SQM) might be the ground state of strongly interacting matter, which is nowadays called the Witten-Bodmer hypothesis [1,2]. If true, there should exist stable objects of SQM with the baryon number A ranging from a few to ∼10 57 . Customarily, small SQM nuggets with A 10 7 are often referred to as strangelets [3][4][5][6][7][8][9][10], or slets [11], while stars consisting of SQM are called strange (quark) stars [12][13][14][15][16][17][18][19][20][21], being possible candidates for pulsars.…”

A Detailed Analysis of the Special Points on $M-R$ Solutions of Hybrid (Twin) Stars

“…In this context, we obtain twin star configurations and special points (SPs) on the M − R diagram with all the considered hadronic models. Several works have suggested that phase transition from hadronic to unpaired or color-flavor locked quark matter often leads to the formation of a "third family" of compact stars [8,17,27,55,[62][63][64][65][66][67][68][69][70][71][72] and twin star configurations under certain circumstances of strong first order phase transitions mainly with considerable density jumps. The M −R plot in such cases often show non-identical branches with two distinct maxima at two different radii.…”

“…Ref. [72] studied smooth phase transition with Gibbs construction and obtained SPs on the mass-radius diagram for different values of the bag constant. In the present work with the considered number of hadronic models and for different values of B as for density-dependent bag model, we have achieved phase transition with Maxwell construction and analyzed the properties of HSs.…”