Gravitational Waveforms

Case A: Irrotational

The gravitational wavetrain from an NSNS merger may be separated into four qualitatively different phases: the inspiral, merger, HMNS spindown and BH ringdown. During the inspiral phase, which takes up most of the binary's lifetime, gravity wave emission gradually reduces the binary separation. The merger phase of the gravitational wavetrain is characterized by tidal disruption of the neutron star, followed by the formation of a hypermassive neutron star (HMNS). As the HMNS spins down, it pulses and emits GWs. After the HMNS undergoes delayed collapse to a spinning BH, ringdown radiation is emitted as the distorted BH settles down to Kerr-like equilibrium (Note: Only in the case of a vacuum spacetime does the spinning BH obey the exact Kerr solution. The BHs formed here are surrounded by gaseous disks with small, but nonnegligible, rest mass). The h_× polarization mode of the gravitational wave is shown below.

h_× Polarization (Lower Hemisphere)

Here, we have a binary neutron star system, with the neutron stars going under tidal disruption. Shown below is h_× in the lower hemisphere. Waveforms are plotted in the region of $r/M \geq 68$.

Fig. 1-1: t/M = 224	Fig. 1-2: t/M = 454	Fig. 1-3: t/M = 698
Fig. 1-4: t/M = 1224	Fig. 1-5: t/M = 1533	Fig. 1-6: t/M = 1823