Revisiting the stability of strange-dwarf stars and strange planets

The dynamical stability of strange-dwarf hybrid stars and strange planets, constituted by strange-quark-matter cores and dilute-nuclear-matter crusts, is revisited by analyzing the fundamental mode eigenfrequencies of the radial oscillation equations with boundary conditions for slow (rapid) conversions originating at the density-discontinuous interface characterizing extremely large (small) microscopic timescales compared to the oscillation periods. For the hadronic crust we used an analytic fit of the BPS results matched to the massless MIT bag model. For the rapid case, our calculations indicate that the zero mode is the so-called {\it reaction mode} whose frequency is a complex number, thus ruling out the existence of strange dwarfs (planets) in nature. On the other hand, slow conversions still provide a sizeable stability window which, interestingly, also reproduces the Glendenning-Kettner-Weber results. The robustness of our findings is demonstrated for different transition densities and using an equation of state from perturbative QCD for the ultra-dense core.
Comment: 9 pages, 3 figures. Version published in European Physical Journal A