Oscillatory properties of strange quark stars described by the vector MIT bag model

Author(s)

Lopes, Luiz L., Jimenez, Jose C., Castro, Luis B., Flores, Cesar V.

Abstract

We investigated the radial and non-radial fundamental ($f$) mode oscillations of self-bound (quark) stars obtained after employing the Vector MIT (vMIT) bag model. Within this model, we computed the equation of state for strange quark matter satisfying thermodynamic consistency. This allowed us to obtain the corresponding behavior of the speed of sound, mass-radius relation, and gravitational redshift. In particular, our choice of $G_V$ = 0.30 fm$^2$ produces masses and radii in agreement with recent astronomical data (e.g. from NICER and HESS J1731). In fact, we tested that variations of the remaining vMIT parameters slightly modify this conclusion. Then, we proceeded to compute the radial oscillation frequencies of the $f$-mode, which is tightly connected to the dynamical stability of these compact stars. We found that increments of the $G_V$ parameter have a stabilizing property around the maximal-mass stars for a given stellar family. We also calculated the gravitational-wave frequencies of the non-radial $f$-mode. Our results show that they are restricted to be in the range (1.6 - 1.8) kHz for high-mass stars and to (1.5 - 1.6) kHz for low-mass stars. Finally, we propose a universal relation between these frequencies and the square root of the average density. All these last results are important in distinguishing strange stars from ordinary neutron stars in future gravitational-wave detections coming from compact sources with activated non-radial modes.

Figures

(Color online) EoS (top) and the square of the speed of sound (bottom) for the three parametrizations discussed in the text.

Mass-radius diagram ($M_0$ is the Sun's mass) for SQM stars obtained by solving the TOV equations for the three parameterizations and constraints discussed in the main text.

The gravitational redshift `$z$' versus the SQM star's mass $M$ ($M_0$ is the Sun's mass) for different values of $G_V$.

The $f$-mode frequency ($\nu_0$) versus the gravitational mass $M$ ($M_0$ is the Sun's mass) for different values of $G_V$.

Non-radial $f$-mode frequencies (top) and damping time (bottom) versus the mass $M$ for different values of $G_V$.

The frequency of the fundamental mode is plotted in the upper panel as a function of the square root of the average density for the different EoSs. The linear relation is satisfied for all three EoSs.

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