Identifying QCD Phase Transitions via the Gravitational Wave Frequency from a Supernova Explosion

We investigate the nonradial oscillations of newly born neutron stars (NSs) and strange quark stars (SQSs). This is done with the relativistic nuclear field theory with hyperon degrees of freedom employed to describe the equation of state (EoS) for the stellar matter in NSs, and with both the MIT bag model and the Nambu–Jona-Lasinio model adopted to construct the configurations of the SQSs. We find that the gravitational-mode (g-mode) eigenfrequencies of newly born SQSs are significantly lower than those of NSs, which is independent of models implemented to describe the EoS for the strange quark matter. Meanwhile, the eigenfrequencies of the other modes of nonradial oscillations, e.g., fundamental (f)- and pressure (p)-modes, are much larger than those of the g-mode, and are related to the stiffness of the EoSs. In light of the first direct observation of gravitational waves (GWs), it is promising to employ GWs to identify the QCD phase transition in high-density strong-interaction matter.

Decoupled Embedding Class-One Strange Stars in Self-Interacting Brans–Dicke Gravity

This work aims to extend two isotropic solutions to the anisotropic domain by decoupling the field equations in self-interacting Brans–Dicke theory. The extended solutions are obtained by incorporating an additional source in the isotropic fluid distribution. We deform the radial metric potential to disintegrate the system of field equations into two sets such that each set corresponds to only one source (either isotropic or additional). The system related to the anisotropic source is solved by employing the MIT bag model as an equation of state. Further, we develop two isotropic solutions by plugging well-behaved radial metric potentials in Karmarkar’s embedding condition. The junction conditions at the surface of the star are imposed to specify the unknown constants appearing in the solution. We examine different physical characteristics of the constructed quark star models by using the mass and radius of PSR J1903+327. It is concluded that, in the presence of a massive scalar field, both stellar structures are well-behaved, viable and stable for smaller values of the decoupling parameter.

Analysis of strange quark stars in massive Brans–Dicke gravity

In this paper, we explore the behavior and anisotropic structure of quark stellar models in the framework of massive Brans–Dicke gravity. The system of field equations, representing a static sphere, is formulated by incorporating the MIT bag model. We use the Karmarkar condition for embedding class-one to formulate a relativistic model corresponding to a well-behaved radial metric function. The values of unknown parameters are determined through the matching of internal and external space–times at the hypersurface. The observed masses and radii of the strange star candidates (RXJ 1856-37, Her X-1 and PSR J1614-2230) specify the solution. Further, we evaluate the impact of the massive scalar field on state parameters and investigate the viability as well as stability of the self-gravitating objects. It is found that the obtained values of the bag constant (corresponding to each star) lie within the accepted range. Moreover, the anisotropic structure meets the necessary viability and stability criteria.

Reduction of the Mass of the Proto-Quark Star during Cooling

The integral parameters (mass, radius) of hot proto-quark stars that are formed in supernova explosion are studied. We use the MIT bag model to determine the pressure of up-down and strage quark matter at finite temperature and in the regime where neutrinos are trapped. It is shown that such stars are heated to temperatures of the order of tens of MeV. The maximum possible values of the central temperatures of these stars are determined. It is shown that the energy of neutrinos that are emitted from proto-quark stars is of the order of 250÷300 MeV. Once formed, the proto-quark stars cool by neutrino emission, which leads to a decrease in the mass of these stars by about 0.16–0.25 M⊙ for stars with the rest masses that are in the range Mb=1.22−1.62M⊙.