Finite-temperature equations of state for neutron star mergers

The detection of gravitational waves from a neutron star merger has opened up the possibility of detecting the presence or creation of deconfined quark matter using the gravitational wave signal. To investigate this possibility, we construct a family of neutron star matter equations of state at nonzero density and temperature by combining state-of-the-art nuclear matter equations of state with holographic equations of state for strongly interacting quark matter. The emerging picture consistently points toward a strong first order deconfinement transition, with a temperature-dependent critical density and latent heat that we quantitatively examine. Recent neutron star mass measurements are further used to discriminate between the different equations of state obtained, leaving a tightly constrained family of preferred equations of state.

Figure 1

Left: The pressures of the DD2 (dashed green curve), IUF (dotted turquoise curve), and SFHx (dashed orange curve) nuclear matter models, shown together with those obtained with the $\mathbf{5}\mathbf{b}$ (red solid curve), $\mathbf{7}\mathbf{a}$ (blue solid curve), and $\mathbf{8}\mathbf{b}$ (black solid curve) potentials of V-QCD, for the temperatures of 6.9 (lower curves) and 75.9 MeV (upper curves). Right: The phase diagram of QCD as suggested by the comparison of the nuclear and quark matter pressures utilized in our work. Corresponding to each of the three nuclear matter EoSs (same color coding as in the left figure), we have three curves corresponding to the V-QCD potentials $\mathbf{5}\mathbf{b}$ (left solid curves), $\mathbf{7}\mathbf{a}$ (middle dashed or dotted curves), and $\mathbf{8}\mathbf{b}$ (right solid curves).

Figure 2

Left: The transition density as a function of temperature, given for the three nuclear physics models considered (same color coding as before). For each nuclear EoS, we again have three curves corresponding to the V-QCD potentials $\mathbf{5}\mathbf{b}$ (lower solid curves), $\mathbf{7}\mathbf{a}$ (middle dashed or dotted curves), and $\mathbf{8}\mathbf{b}$ (upper solid curves). Right: The latent heat of the (first order) deconfinement transition as a function of temperature. The notation follows the left figure.

Figure 3

The speed of sound squared $c_s^2$, or stiffness $dp/d\epsilon$, as a function of baryon density for the nuclear matter models and V-QCD potentials at vanishing temperature. The color codings follow the choices made in Fig. 1 (left), while the dotted lines indicate the transitions between the two descriptions in all combinations of models and potentials (see also Table 1).

Figure 4

The mass-radius curves resulting from each of the three nuclear matter models considered, with the color scheme following the previous figures. The straight line segments correspond to the unstable branches, where the cores are populated by holographic quark matter described by the different V-QCD potentials.