Binary neutron star merger simulations with hot microscopic equations of state

We perform binary neutron star merger simulations using a newly derived set of finite-temperature equations of state in the Brueckner-Hartree-Fock approach. We point out the important and opposite roles of finite temperature and rotation for stellar stability and carry out a detailed study about the gravitational-wave properties, matter distribution, and ejecta properties in the postmerger phase for the different cases. The validity of several universal relations is also examined and the most suitable equations of state are identified.

Figure 1

Gravitational mass vs central density (top row) and radius (bottom row) for static (red curves) and uniformly rotating at $f_{\text{Kepler}}$ (green curves) stars at $T=0$ (solid curves) and $T=50\mathrm{MeV}$ (dashed curves). Configurations of constant baryonic masses $M_B/M_{\odot }$ (numbers) are indicated by markers and connected by thin lines.

Figure 2

Maximum values of rest-mass density (a) and azimuthally-averaged differential rotational frequency (b), maximum $T_{\max }$ and average $T_{\mathrm{av}}$ temperature (c), and disk mass (d) as a function of time for the simulations using the four different EOSs.

Figure 3

Upper panels: gravitational waveforms over a timescale of 15 ms after the merger for the four simulated models obtained for gravitational masses $2\times 1.35M_{\odot }$. Lower panels: the spectrograms for all the considered cases; red lines represent the position of the $f_2$ peaks (Table 2).

Figure 4

PSDs $\tilde{h}$, Eq. (19), of the simulations evaluated at a distance of 100 Mpc. Vertical dashed lines of different colors indicate the frequency of the main postmerger peak $f_2$ and estimated error. The sensitivity curve (magenta color) of Advanced LIGO is displayed for reference.

Figure 5

Upper panel: Enclosed baryonic mass $M_B$ as a function of spherical radius $r$ at $t=15\mathrm{ms}$ for the different EOSs. Thick dashed lines denote radii corresponding to $M_{\mathrm{obj}}$ in Table 2. Thin dashed lines are the radii of $T=50\mathrm{MeV}$ $M_{\max }$ Kepler configurations in Table 1. Lower panel: Azimuthally averaged angular velocity, Eq. (26), as a function of the radial cylindrical coordinate $r$ (at $z=0$) at $t=15\mathrm{ms}$. Thin horizontal dashed lines indicate the Kepler frequencies of the $T=50\mathrm{MeV}$ $M_{\max }$ configurations for the different EOSs listed in Table 1.

Figure 6

Distribution of the ejected mass as functions of the polar angle $\theta$ (a), velocity ratio $v/c$ (b), electron fraction $Y_e$ (c), and specific entropy $s$ (d). Curves are normalized with respect to the total ejected mass values $M_{\mathrm{ej}}$ enlisted in Table 2.