Gravitational waves from very massive stars collapsing to a black hole

We compute gravitational waves emitted by the collapse of a rotating very massive star (VMS) core leading directly to a black hole in axisymmetric numerical-relativity simulations. The evolved rotating VMS is derived by a stellar evolution calculation, and its initial mass and the final carbon-oxygen core mass are 320 M-circle dot and approximate to 150 M-circle dot, respectively. We find that, for the moderately rapidly rotating cases, the peak strain amplitude and the corresponding frequency of gravitational waves are similar to 10(-22) and f approximate to 300-600 Hz for an event at the distance of D = 50 Mpc. Such gravitational waves will be detectable only for D less than or similar to 10 Mpc by second-generation detectors, advanced LIGO, advanced VIRGO, and KAGRA, even if the designed sensitivity for these detectors is achieved. However, third-generation detectors will be able to detect such gravitational waves for an event up to D similar to 100 Mpc. The detection of the gravitational-wave signal will provide a potential opportunity for verifying the presence of VMSs with mass greater than or similar to 300 M-circle dot and their pair-unstable collapse in the Universe.