  We present numerical results of three-dimensional simulations for the merger
of binary neutron stars (BNSs) in full general relativity. Hybrid equations of
state (EOSs) are adopted to mimic realistic nuclear EOSs. In this approach, we
divide the EOSs into two parts, i.e., the thermal part and the cold part. For
the cold part, we assign a fitting formula for realistic EOSs of cold nuclear
matter slightly modifying the formula developed by Haensel and Potekhin. We
adopt the SLy and FPS EOSs for which the maximum allowed ADM mass of cold and
spherical neutron stars (NSs) is ~ 2.04Mo and 1.80Mo, respectively. Simulations
are performed for BNSs of the total ADM mass in the range between 2.4Mo and
2.8Mo with the rest-mass ratio Q_M to be in the range 0.9 < Q_M < 1. It is
found that if the total ADM mass of the system is larger than a threshold
M_{thr}, a black hole (BH) is promptly formed in the merger irrespective of the
mass ratios. In the other case, the outcome is a hypermassive NS of a large
ellipticity, which results from the large adiabatic index of the realistic EOSs
adopted. The value of M_{thr} depends on the EOS: ~ 2.7Mo and ~ 2.5Mo for the
SLy and FPS EOSs, respectively. Gravitational waves are computed in terms of a
gauge-invariant wave extraction technique. In the formation of the hypermassive
NS, quasiperiodic gravitational waves of a large amplitude and of frequency
between 3 and 4 kHz are emitted. The estimated emission time scale is < 100 ms,
after which the hypermassive NS collapses to a BH. Because of the long emission
time, the effective amplitude may be large enough to be detected by advanced
laser interferometric gravitational wave detectors if the distance to the
source is smaller than ~ 100 Mpc.
