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This theoretical study rigorously proves the mathematical equivalence between two different stability criteria for neutron stars mixed with dark matter: the zero-frequency oscillation mode and the static critical-curve criterion. The authors demonstrate that stable dark matter-admixed neutron stars form a surface in three-dimensional parameter space, allowing for the existence of "twin stars" that have identical observable properties (mass and radius) but different internal compositions. This framework extends to general multi-fluid stellar systems beyond the specific case of dark matter admixture.
Why it matters
The results provide a theoretical foundation for using astronomical observations of neutron stars to constrain the properties of dark matter. The possibility of twin stars with identical external characteristics but different internal structures has important implications for interpreting compact star measurements and could help distinguish between different models of dense matter physics.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Abstract: Regarding the stability of two-fluid star models, we rigorously prove the equivalence between the emergence of a zero-frequency radial oscillation mode and the static critical-curve criterion for mixed stars, after briefly reviewing the hybrid star case. This establishes a sufficient-condition relation between two independently developed stability criteria. Although this connection has often been implicitly assumed in previous studies of mixed stars, it has rarely been demonstrated explicitly. Our derivation can be extended to general multi-fluid systems. As an illustrative example, we consider dark matter-admixed neutron star models and show that their stability boundary differs from that of single-fluid stars. In this case, stable configurations form a surface in the three-dimensional parameter space spanned by central pressure, mass, and radius, giving rise to a class of stable mixed stars. This class includes “twin stars” with identical masses and radii but distinct internal compositions and structures. These results provide a useful framework for interpreting compact star observations and for constraining dark matter properties through astrophysical measurements.
Source: Stability Boundary of Neutron-Dark Matter Mixed Stars