Phase Transition to Hyperon Matter in Neutron Stars

Recent progress in the understanding of the high density phase of neutron stars advances the view that a substantial fraction of the matter consists of hyperons. The possible impacts of a highly attractive interaction between hyperons on the properties of compact stars are investigated. We find that a hadronic equation of state with hyperons allows for a first order phase transition to hyperonic matter. The corresponding hyperon stars can have rather small radii of $R\approx 8\mathrm{k}\mathrm{m}$.

Figure 1

Equation of state of strange hadronic matter for different strengths of the hyperon-hyperon interactions. A second stable minimum appears at large strangeness fraction $f_s$ which can be deeper than ordinary matter.

Figure 2

Equation of state in $\beta$ equilibrium (neutron star matter) for different strengths of the hyperon-hyperon interactions.

Figure 3

Mass-radius relation for neutron stars with a highly attractive hyperon-hyperon interaction.

Figure 4

The total baryon number $N_B$ versus the gravitational mass $M/M_{\odot }$.