http://arxiv.org/abs/1607.03984
The influence of the anisotropy in the equilibrium and stability of strange stars is investigated through the numerical solution of the hydrostatic equilibrium equation and the radial oscillation equation, both modified from their original version to include this effect. The strange matter inside the quark stars is described by the MIT bag model equation of state. For the anisotropy two different kinds of local anisotropic $\sigma=p_t-p_r$, where $p_t$ and $p_r$ are respectively the tangential and the radial pressure, are considered: one that is null at the star’s surface defined by $p_r(R)=0$, and other that is nonnull on it, namely, $\sigma_s=0$ and $\sigma_s\neq0$. In the case $\sigma_s=0$, the maximum mass value and the zero frequency of oscillation are found at the same central energy density, indicating that the maximum mass marks the onset of the instability. For the case $\sigma_s\neq0$, we show that only in a sequence of equilibrium configurations with the same value of $\sigma_s$, the maximum mass point and the zero frequency of oscillation coincide in the same central energy density value. Thus, only when the tangential pressure is maintained fixed at the star surface’s $p_t(R)$, the stability star regions are determined always by the condition $dM/d\rho_c>0$. These results are also quite important to analyze the stability of other anisotropic compact objects such as neutron stars, boson stars and gravastars.
J. Arbanil and M. Malheiro
Fri, 15 Jul 16
10/54
Comments: 17 pages, 21 figures
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