When the orbital radius falls below

When the orbital radius falls below the Innermost Stable Circular Orbit (ISCO), stable circular orbits are no longer allowed and the binary stars eventually plunge toward each other and merge. A binary system of two neutron stars for example is expected to reach a frequency of about 800 Hz by the time the radius reaches the ISCO. Computation of merging neutron stars or black holes is quite challenging in terms of computation costs and thus numerous efforts have been made to calculate these dynamics and associated gravitational radiation waveform with supercomputers [5]. The merger of the binary stars results in a highly deformed single black hole which sheds its deformity by emitting gravitational waves referred to as ring-down signals.