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 { 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 , { SNR } > 35 is needed .
The standard model of Pop III population synthesis tells us that the event rate for the confirmation of more than 50 \% of the ergoregion by the second generation gravitational wave detectors is \sim 2.3 { events~ { } yr ^ { -1 } ~ { } ( SFR _ { p } / ( 10 ^ { -2.5 } ~ { } M _ { \odot } ~ { } yr ^ { -1 } ~ { } Mpc ^ { -3 } ) ) % } \cdot ( [ f _ { b } / ( 1 + f _ { b } ) ] / 0.33 ) where { SFR _ { p } } and { f _ { b } } are the peak value of the Pop III star formation rate and the fraction of binaries , respectively .