Skyrmion Stars: Astrophysical Motivations and Implications

We study mass-radius relations for compact stars employing an equation ofstate (EOS) of dense matter based on a Skyrme fluid. The zero-temperaturemean-field model is based on mesonic excitations, incorporates the scalebreaking of QCD, and accommodates baryons (nucleons) which arise as a solitonicconfiguration of mesonic fields. Stable configurations are obtained for centraldensities $\rho_c/\rho_n\leq 5.0$ where $\rho_n=2.575\times 10^{14}$ g/cc isthe nuclear saturation density. These {\it Skyrmion Stars} are mostly fluid,with a crust which we describe by the EOS of Baym, Pethick and Sutherland.Their masses and radii are in the range $0.4 \le M/M_{\odot} \le 3.6$ and $13{\rm km} \le R \le 23 {\rm km}$, respectively. The minimum spin period iscomputed to be between $0.7 {\rm ms}\le P \le 2.1 {\rm ms}$. They appear tohave a mass-radius curve quite different from either neutron or quark stars,and provide a suitable description of the heavier mass neutron stars discoveredrecently due to the inherently stiff EOS. Within the same model, we compute thedominant neutrino emissivity in neutron-rich $\beta$-equilibrated matter, anddetermine the cooling behaviour of Skyrmion stars.Comment: 28 pages and 5 figures; this version to appear in the Astrophysical Journa