Possible confirmation of the existence of ergoregion by the Kerr quasinormal mode in gravitational waves from Pop III massive black hole binary

Understand

The existence of the ergoregion of the Kerr space-time has not been confirmed observationally yet.

• We show that the confirmation would be possible by observing the quasinormal mode in gravitational waves.
• As an example, using the recent population synthesis results of Pop III binary black holes, we find that the peak of the final merger mass ($M_f$) is about $50~\rm M_{\odot}$, while the fraction of the final spin $q_f = a_f/M_f > 0.7$ needed for the confirmation of a part of ergoregion is $\sim 77\%$.
• To confirm the frequency of the quasinormal mode, ${\rm SNR} > 35$ is needed.