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Skyrmion Stars: Astrophysical Motivations and Implications

We study mass-radius relations for compact stars employing an equation of state (EOS) of dense matter based on a Skyrme fluid. The zero-temperature mean-field model is based on mesonic excitations, incorporates the scale breaking of QCD, and accommodates baryons (nucleons) that arise as a solitonic configuration of mesonic fields. Stable configurations are obtained for central densities ρc/ρn ≤ 5.0, where ρn = 2.575 × 1014 g cm-3 is the nuclear saturation density. These "skyrmion stars" are mostly fluid, with a crust that we describe by the EOS of Baym, Pethick, & Sutherland. Their masses and radii are in the ranges 0.4 ≤ M/M☉ ≤ 3.6 and 13 km ≤ R ≤ 23 km, respectively. The minimum spin period is computed to be in the range 0.7 ms ≤ P ≤ 2.1 ms. They appear to have a mass-radius curve quite different from either neutron or quark stars and provide a suitable description of the heavier mass neutron stars discovered recently due to the inherently stiff EOS. Within the same model, we compute the dominant neutrino emissivity in neutron-rich β-equilibrated matter and determine the cooling behavior of skyrmion stars.