We have studied the t-J model using the Green function Monte Carlo technique. We have obtained accurate energies well converged in the thermodynamic limit by performing simulations for up to 242 lattice sites. By studying the energy as a function of hole doping we conclude that there is no phase separation in the physical region relevant for high- Tc superconductors. This finding is further supported by the hole-hole correlation function calculation. Remarkably, near the phase separation instability, for Jc/t ∼ 0.5 this function displays enhanced fluctuations at incommensurate wave vectors that scale linearly with the doping, in agreement with experimental findings.
